<?xml version="1.0"?>

<!--
  Copyright (C) Nginx, Inc.
  -->

<!DOCTYPE article SYSTEM "../../../../dtd/article.dtd">

<article name="Reference"
        link="/en/docs/njs/reference.html"
        lang="en"
        rev="45">

<section id="summary">

<para>
<link doc="index.xml">njs</link> provides objects, methods and properties
for extending nginx functionality.
</para>

</section>


<section id="http_stream" name="nginx objects">


<section id="http" name="HTTP Request">

<para>
The HTTP request object is available only in the
<link doc="../http/ngx_http_js_module.xml">ngx_http_js_module</link> module.
All string properties of the object are <link id="string">byte strings</link>.

<list type="tag">

<tag-name id="r_args"><literal>r.args{}</literal></tag-name>
<tag-desc>
request arguments object, read-only
</tag-desc>

<tag-name><literal>r.error(<value>string</value>)</literal></tag-name>
<tag-desc>
writes a <literal>string</literal> to the error log
on the <literal>error</literal> level of logging
</tag-desc>

<tag-name><literal>r.finish()</literal></tag-name>
<tag-desc>
finishes sending a response to the client
</tag-desc>

<tag-name id="r_headers_in"><literal>r.headersIn{}</literal></tag-name>
<tag-desc>
incoming headers object, read-only.
<para>
The <literal>Foo</literal> request header
can be accessed with the syntax:
<literal>headersIn.foo</literal> or <literal>headersIn['Foo']</literal>.
</para>

<para>
The 
<header>Authorization</header>,
<header>Content-Length</header>,
<header>Content-Range</header>,
<header>Content-Type</header>,
<header>ETag</header>,
<header>Expect</header>,
<header>From</header>,
<header>Host</header>,
<header>If-Match</header>,
<header>If-Modified-Since</header>,
<header>If-None-Match</header>,
<header>If-Range</header>,
<header>If-Unmodified-Since</header>,
<header>Max-Forwards</header>,
<header>Proxy-Authorization</header>,
<header>Referer</header>,
<header>Transfer-Encoding</header>, and
<header>User-Agent</header>
request headers can have only one field value
(<link doc="changes.xml" id="njs0.4.1">0.4.1</link>).
Duplicate field values in <header>Cookie</header> headers
are separated by semicolon (<literal>;</literal>).
Duplicate field values in all other request headers are separated by commas.
</para>
</tag-desc>

<tag-name id="r_headers_out"><literal>r.headersOut{}</literal></tag-name>
<tag-desc>
outgoing headers object, writable.
<para>
The <header>Foo</header> response header
can be accessed with the syntax:
<literal>headersOut.foo</literal> or <literal>headersOut['Foo']</literal>.
</para>

<para>
Field values of multi-value response headers
(<link doc="changes.xml" id="njs0.4.0">0.4.0</link>)
can be set with the syntax:
<example>
r.headersOut['Foo'] = ['a', 'b']
</example>
where the output will be:
<example>
Foo: a
Foo: b
</example>
All previous field values of the <header>Foo</header> response header
will be deleted.
</para>

<para>
For standard response headers
that accept only a single field value such as
<header>Content-Type</header>,
only the last element of the array will take effect.
Field values of the <header>Set-Cookie</header> response header
are always returned as an array.
Duplicate field values in
<header>Age</header>,
<header>Content-Encoding</header>,
<header>Content-Length</header>,
<header>Content-Type</header>,
<header>ETag</header>,
<header>Expires</header>,
<header>Last-Modified</header>,
<header>Location</header>,
<header>Retry-After</header>
response headers are ignored.
Duplicate field values in all other response headers
are separated by commas.
</para>
</tag-desc>

<tag-name><literal>r.httpVersion</literal></tag-name>
<tag-desc>
HTTP version, read-only
</tag-desc>

<tag-name id="r_internal_redirect"><literal>r.internalRedirect(<value>uri</value>)</literal></tag-name>
<tag-desc>
performs an internal redirect to the specified <literal>uri</literal>.
If the uri starts with the “<literal>@</literal>” prefix,
it is considered a named location.
The actual redirect happens after the handler execution is completed.
</tag-desc>

<tag-name><literal>r.log(<value>string</value>)</literal></tag-name>
<tag-desc>
writes a <literal>string</literal> to the error log
on the <literal>info</literal> level of logging
</tag-desc>

<tag-name><literal>r.method</literal></tag-name>
<tag-desc>
HTTP method, read-only
</tag-desc>

<tag-name id="r_parent"><literal>r.parent</literal></tag-name>
<tag-desc>
references the parent request object
</tag-desc>

<tag-name><literal>r.remoteAddress</literal></tag-name>
<tag-desc>
client address, read-only
</tag-desc>

<tag-name id="r_raw_headers_in"><literal>r.rawHeadersIn{}</literal></tag-name>
<tag-desc>
returns an array of key-value pairs
exactly as they were received from the client
(<link doc="changes.xml" id="njs0.4.1">0.4.1</link>).
<para>
For example, with the following request headers:
<example>
Host: localhost
Foo:  bar
foo:  bar2
</example>
the output of <literal>r.rawHeadersIn</literal> will be:
<example>
[
    ['Host', 'localhost'],
    ['Foo', 'bar'],
    ['foo', 'bar2']
]
</example>
All <literal>foo</literal> headers
can be collected with the syntax:
<example>
r.rawHeadersIn.filter(v=>v[0].toLowerCase() == 'foo').map(v=>v[1])
</example>
the output will be:
<example>
['bar', 'bar2']
</example>
Header field names are not converted to lower case,
duplicate field values are not merged.
</para>
</tag-desc>

<tag-name id="r_raw_headers_out"><literal>r.rawHeadersOut{}</literal></tag-name>
<tag-desc>
returns an array of key-value pairs of response headers
(<link doc="changes.xml" id="njs0.4.1">0.4.1</link>).
Header field names are not converted to lower case,
duplicate field values are not merged.
</tag-desc>

<tag-name id="r_request_body"><literal>r.requestBody</literal></tag-name>
<tag-desc>
returns the client request body if it has not been
written to a temporary file.
To ensure that the client request body is in memory,
its size should be limited by
<link doc="../http/ngx_http_core_module.xml" id="client_max_body_size"/>,
and a sufficient buffer size should be set using
<link doc="../http/ngx_http_core_module.xml" id="client_body_buffer_size"/>.
The property is available only in the
<link doc="../http/ngx_http_js_module.xml" id="js_content"/> directive.
</tag-desc>

<tag-name id="r_response_body"><literal>r.responseBody</literal></tag-name>
<tag-desc>
holds the <link id="subrequest">subrequest</link> response body, read-only.
The size of <literal>r.responseBody</literal> is limited by the
<link doc="../http/ngx_http_core_module.xml" id="subrequest_output_buffer_size"/>
directive.
</tag-desc>

<tag-name><literal>r.return(status[, string])</literal></tag-name>
<tag-desc>
sends the entire response
with the specified <literal>status</literal> to the client
<para>
It is possible to specify either a redirect URL
(for codes 301, 302, 303, 307, and 308)
or the response body text (for other codes) as the second argument
</para>
</tag-desc>

<tag-name><literal>r.send(<value>string</value>)</literal></tag-name>
<tag-desc>
sends a part of the response body to the client
</tag-desc>

<tag-name><literal>r.sendHeader()</literal></tag-name>
<tag-desc>
sends the HTTP headers to the client
</tag-desc>

<tag-name><literal>r.status</literal></tag-name>
<tag-desc>
status, writable
</tag-desc>

<tag-name id="subrequest"><literal>r.subrequest(<value>uri</value>[,
<value>options</value>[, <value>callback</value>]])</literal></tag-name>
<tag-desc>
creates a subrequest with the given <literal>uri</literal> and
<literal>options</literal>, and installs
an optional completion <literal>callback</literal>.

<para>
A
<link doc="../dev/development_guide.xml.xml" id="http_subrequests">subrequest</link>
shares its input headers with the client request.
To send headers different from original headers to a proxied server, the
<link doc="../http/ngx_http_proxy_module.xml" id="proxy_set_header"/>
directive can be used.
To send a completely new set of headers to a proxied server, the
<link doc="../http/ngx_http_proxy_module.xml" id="proxy_pass_request_headers"/>
directive can be used.
</para>

<para>
If <literal>options</literal> is a string, then it
holds the subrequest arguments string.
Otherwise, <literal>options</literal> is expected to be
an object with the following keys:
<list type="tag">
<tag-name><literal>args</literal></tag-name>
<tag-desc>
arguments string, by default an empty string is used
</tag-desc>
<tag-name><literal>body</literal></tag-name>
<tag-desc>
request body,
by default the request body of the parent request object is used
</tag-desc>

<tag-name><literal>method</literal></tag-name>
<tag-desc>
HTTP method, by default the <literal>GET</literal> method is used
</tag-desc>

<tag-name><literal>detached</literal></tag-name>
<tag-desc>
boolean flag (<link doc="changes.xml" id="njs0.3.9">0.3.9</link>),
if <literal>true</literal>, the created subrequest is a detached subrequest.
Responses to detached subrequests are ignored.
Unlike ordinary subrequests, a detached subrequest
can be created inside a variable handler.
The detached flag and callback argument are mutually exclusive.
</tag-desc>

</list>
</para>

<para>
The completion <literal>callback</literal> receives
a subrequest response object with methods and properties
identical to the parent request object.
</para>

<para>
Since <link doc="changes.xml" id="njs0.3.8">0.3.8</link>,
if a <literal>callback</literal> is not provided,
the <literal>Promise</literal> object
that resolves to the subrequest response object is returned.
</para>
</tag-desc>

<tag-name id="r_uri"><literal>r.uri</literal></tag-name>
<tag-desc>
current <link doc="../http/ngx_http_core_module.xml" id="var_uri">URI</link>
in request,
<link doc="../http/ngx_http_core_module.xml" id="location">normalized</link>,
read-only
</tag-desc>

<tag-name id="r_variables"><literal>r.variables{}</literal></tag-name>
<tag-desc>
nginx variables object,
writable (since <link doc="changes.xml" id="njs0.2.8">0.2.8</link>)
</tag-desc>

<tag-name><literal>r.warn(<value>string</value>)</literal></tag-name>
<tag-desc>
writes a <literal>string</literal> to the error log
on the <literal>warning</literal> level of logging
</tag-desc>

</list>
</para>

</section>


<section id="stream" name="Stream Session">

<para>
The stream session object is available only in the
<link doc="../stream/ngx_stream_js_module.xml">ngx_stream_js_module</link>
module.
All string properties of the object are <link id="string">byte strings</link>.
</para>

<para>
<list type="tag">

<tag-name id="s_allow"><literal>s.allow()</literal></tag-name>
<tag-desc>
successfully finalizes the phase handler
(<link doc="changes.xml" id="njs0.2.4">0.2.4</link>)
</tag-desc>

<tag-name id="s_decline"><literal>s.decline()</literal></tag-name>
<tag-desc>
finalizes the phase handler and passes control to the next handler
(<link doc="changes.xml" id="njs0.2.4">0.2.4</link>)
</tag-desc>

<tag-name id="s_deny"><literal>s.deny()</literal></tag-name>
<tag-desc>
finalizes the phase handler with the access error code
(<link doc="changes.xml" id="njs0.2.4">0.2.4</link>)
</tag-desc>

<tag-name id="s_done"><literal>s.done</literal>(<value>[code]</value>)</tag-name>
<tag-desc>
successfully finalizes the current phase handler
or finalizes it with the specified numeric code
(<link doc="changes.xml" id="njs0.2.4">0.2.4</link>).
</tag-desc>

<tag-name><literal>s.error(<value>string</value>)</literal></tag-name>
<tag-desc>
writes a sent <literal>string</literal> to the error log
on the <literal>error</literal> level of logging
</tag-desc>

<tag-name><literal>s.log(<value>string</value>)</literal></tag-name>
<tag-desc>
writes a sent <value>string</value> to the error log
on the <literal>info</literal> level of logging
</tag-desc>

<tag-name id="s_off"><literal>s.off(<value>eventName</value>)</literal></tag-name>
<tag-desc>
unregisters the callback set by the <link id="s_on">s.on()</link> method
(<link doc="changes.xml" id="njs0.2.4">0.2.4</link>)
</tag-desc>

<tag-name id="s_on"><literal>s.on(<value>event</value>,
<value>callback</value>)</literal></tag-name>
<tag-desc>
registers a <literal>callback</literal> for the specified <literal>event</literal>
(<link doc="changes.xml" id="njs0.2.4">0.2.4</link>).

<para>
An <literal>event</literal> may be one of the following strings:
<list type="tag">
<tag-name><literal>upload</literal></tag-name>
<tag-desc>
new data from a client
</tag-desc>

<tag-name><literal>download</literal></tag-name>
<tag-desc>
new data to a client
</tag-desc>

</list>
</para>

<para>
The completion callback has the following prototype:
<literal>callback(data, flags)</literal>, where
<literal>data</literal> is string,
<literal>flags</literal> is an object
with the following properties:
<list type="tag">
<tag-name id="s_on_callback_last"><literal>last</literal></tag-name>
<tag-desc>
a boolean value, true if data is a last buffer.
</tag-desc>

</list>
</para>
</tag-desc>

<tag-name><literal>s.remoteAddress</literal></tag-name>
<tag-desc>
client address, read-only
</tag-desc>

<tag-name id="s_send"><literal>s.send(<value>data</value>[,
<value>options</value>])</literal></tag-name>
<tag-desc>
sends the data to the client
(<link doc="changes.xml" id="njs0.2.4">0.2.4</link>).
The <literal>options</literal> is an object used
to override nginx buffer flags derived from an incoming data chunk buffer.
The flags can be overriden with the following flags:
<para>
<list type="tag">

<tag-name><literal>last</literal></tag-name>
<tag-desc>
boolean, true if the buffer is the last buffer
</tag-desc>

<tag-name><literal>flush</literal></tag-name>
<tag-desc>
boolean, true if the buffer should have the <literal>flush</literal> flag
</tag-desc>
</list>
</para>
The method can be called multiple times per callback invocation.
</tag-desc>

<tag-name id="s_variables"><literal>s.variables{}</literal></tag-name>
<tag-desc>
nginx variables object, writable
(since <link doc="changes.xml" id="njs0.2.8">0.2.8</link>)
</tag-desc>

<tag-name><literal>s.warn(<value>string</value>)</literal></tag-name>
<tag-desc>
writes a sent <literal>string</literal> to the error log
on the <literal>warning</literal> level of logging
</tag-desc>

</list>
</para>

</section>

</section>


<section id="core" name="Core">


<section id="core_global" name="Global">


<section id="process" name="Process">

<para>
The <literal>process</literal> object is a global object
that provides information about the current process
(<link doc="changes.xml" id="njs0.3.3">0.3.3</link>).
</para>


<para>
<list type="tag">

<tag-name id="process_argv"><literal>process.argv</literal></tag-name>
<tag-desc>
Returns an array that contains the command line arguments
passed when the current process was launched.
</tag-desc>

<tag-name id="process_env"><literal>process.env</literal></tag-name>
<tag-desc>
Returns an object containing the user environment.
<note>
By default, nginx removes all environment variables inherited
from its parent process except the TZ variable.
Use the <link doc="../ngx_core_module.xml" id="env"/> directive
to preserve some of the inherited variables.
</note>
</tag-desc>

<tag-name id="process_pid"><literal>process.pid</literal></tag-name>
<tag-desc>
Returns the PID of the current process.
</tag-desc>

<tag-name id="process_ppid"><literal>process.ppid</literal></tag-name>
<tag-desc>
Returns the PID of the current parent process.
</tag-desc>

</list>
</para>

</section>

</section>


<section id="core_object" name="Object">

<para>
The <literal>Object</literal> constructor corresponds to a standard JS object.
<list type="tag">

<tag-name id="object_entries"><literal>Object.entries(<value>object</value>)</literal></tag-name>
<tag-desc>
returns an array of all enumerable property
<literal>[key, value]</literal> pairs
of the given <literal>object</literal>
(<link doc="changes.xml" id="njs0.2.7">0.2.7</link>).
</tag-desc>

<tag-name id="object_values"><literal>Object.values(<value>object</value>)</literal></tag-name>
<tag-desc>
returns an array of all enumerable property values
of the given <literal>object</literal>
(<link doc="changes.xml" id="njs0.2.7">0.2.7</link>).
</tag-desc>

</list>
</para>

</section>


<section id="string" name="String">

<para>
There are two types of strings in njs: a Unicode string (default) and
a byte string.
</para>

<para>
A Unicode string corresponds to an ECMAScript string
which contains Unicode characters.
</para>

<para>
Byte strings contain a sequence of bytes
and are used to serialize Unicode strings
to external data and deserialize from external sources.
For example, the <link id="string_toutf8">toUTF8()</link> method serializes
a Unicode string to a byte string using UTF8 encoding:
<example>
>> '£'.toUTF8().toString('hex')
'c2a3'  /* C2 A3 is the UTF8 representation of 00A3 ('£') code point */
</example>
The <link id="string_tobytes">toBytes()</link> method serializes
a Unicode string with code points up to 255 into a byte string,
otherwise, <literal>null</literal> is returned:
<example>
>> '£'.toBytes().toString('hex')
'a3'  /* a3 is a byte equal to 00A3 ('£') code point  */
</example>
Only byte strings can be converted to different encodings.
For example, a string cannot be encoded to <literal>hex</literal> directly:
<example>
>> 'αβγδ'.toString('base64')
TypeError: argument must be a byte string
    at String.prototype.toString (native)
    at main (native)
</example>
To convert a Unicode string to hex,
first, it should be converted to a byte string and then to hex:
<example>
>> 'αβγδ'.toUTF8().toString('base64')
'zrHOss6zzrQ='
</example>

<list type="tag">

<tag-name id="string_bytesfrom"><literal>String.bytesFrom(<value>array</value>
| <value>string</value>, <value>encoding</value>)</literal></tag-name>
<tag-desc>
(njs specific) Creates a byte string either from an array that contains octets,
or from an encoded string
(<link doc="changes.xml" id="njs0.2.3">0.2.3</link>).
The encoding can be
<literal>hex</literal>,
<literal>base64</literal>, and
<literal>base64url</literal>.
<example>
>> String.bytesFrom([0x62, 0x75, 0x66, 0x66, 0x65, 0x72])
'buffer'

>> String.bytesFrom('YnVmZmVy', 'base64')
'buffer'
</example>
</tag-desc>

<tag-name id="string_fromcharcode"><literal>String.fromCharCode(<value>CharCode1</value>[, ...[,
<value>CharCodeN</value>]])</literal></tag-name>
<tag-desc>
Returns a string from one or more Unicode code points.
<example>
>> String.fromCharCode(97, 98, 99, 100)
'abcd'
</example>
</tag-desc>

<tag-name id="string_fromcodepoint"><literal>String.fromCodePoint(<value>codePoint1</value>[, ...[,
<value>codePoint2</value>]])</literal></tag-name>
<tag-desc>
Returns a string from one or more Unicode code points.
<example>
>> String.fromCodePoint(97, 98, 99, 100)
'abcd'
</example>
</tag-desc>

<tag-name id="string_charat"><literal>String.prototype.charAt(<value>index</value>)</literal></tag-name>
<tag-desc>
Returns a string representing one Unicode code unit
at the specified <literal>index</literal>;
empty string if index is out of range.
The index can be an integer
between 0 and 1-less-than the length of the string.
If no index is provided, the default is <literal>0</literal>,
so the first character in the string is returned.
</tag-desc>

<tag-name id="string_codepointat"><literal>String.prototype.CodePointAt(<value>position</value>)</literal></tag-name>
<tag-desc>
Returns a number representing the code point value of the character
at the given <literal>position</literal>;
<literal>undefined</literal> if there is no element at position.
<example>
>> 'ABCD'.codePointAt(3);
68
</example>
</tag-desc>

<tag-name id="string_concat"><literal>String.prototype.concat(<value>string1</value>[, ...,
<value>stringN</value>])</literal></tag-name>
<tag-desc>
Returns a string that contains the concatenation of specified
<literal>strings</literal>.
<example>
>> "a".concat("b", "c")
'abc'
</example>
</tag-desc>

<tag-name id="string_endswith"><literal>String.prototype.endsWith(<value>searchString</value>[,
<value>length</value>])</literal></tag-name>
<tag-desc>
Returns <literal>true</literal> if a string ends with the characters
of a specified string, otherwise <literal>false</literal>.
The optional <literal>length</literal> parameter is the the length of string.
If omitted, the default value is the length of the string.
<example>
>> 'abc'.endsWith('abc')
true
>> 'abca'.endsWith('abc')
false
</example>
</tag-desc>

<tag-name id="string_frombytes"><literal>String.prototype.fromBytes(<value>start</value>[,
<value>end</value>])</literal></tag-name>
<tag-desc>
(njs specific) Returns a new Unicode string from a byte string
where each byte is replaced with a corresponding Unicode code point.
</tag-desc>

<tag-name id="string_fromutf8"><literal>String.prototype.fromUTF8(<value>start</value>[,
<value>end</value>])</literal></tag-name>
<tag-desc>
(njs specific) Converts a byte string containing a valid UTF8 string
into a Unicode string,
otherwise <literal>null</literal> is returned.
</tag-desc>

<tag-name id="string_includes"><literal>String.prototype.includes(<value>searchString</value>[,
<value>position</value>]))</literal></tag-name>
<tag-desc>
Returns <literal>true</literal> if a string is found within another string,
otherwise <literal>false</literal>.
The optional <literal>position</literal> parameter is the position
within the string at which to begin search for <literal>searchString</literal>. 
Default value is 0.
<example>
>> 'abc'.includes('bc')
true
</example>
</tag-desc>

<tag-name id="string_indexof"><literal>String.prototype.indexOf(<value>searchString</value>[,
<value>fromIndex</value>])</literal></tag-name>
<tag-desc>
Returns the position of the first occurrence
of the <literal>searchString</literal>.
The search is started at <literal>fromIndex</literal>.
Returns <value>-1</value> if the value is not found.
The <literal>fromIndex</literal> is an integer,
default value is 0.
If <literal>fromIndex</literal> is lower than 0
or greater than
<link id="string_length">String.prototype.length</link><value></value>,
the search starts at index <value>0</value> and
<value>String.prototype.length</value>.
<example>
>> 'abcdef'.indexOf('de', 2)
3
</example>
</tag-desc>

<tag-name id="string_lastindexof"><literal>String.prototype.lastIndexOf(<value>searchString</value>[,
<value>fromIndex</value>])</literal></tag-name>
<tag-desc>
Returns the position of the last occurrence
of the <literal>searchString</literal>,
searching backwards from <literal>fromIndex</literal>.
Returns <value>-1</value> if the value is not found.
If <literal>searchString</literal>  is empty,
then <literal>fromIndex</literal> is returned.
<example>
>> "nginx".lastIndexOf("gi")
1
</example>
</tag-desc>

<tag-name id="string_length"><literal>String.prototype.length</literal></tag-name>
<tag-desc>
Returns the length of the string.
<example>
>> 'αβγδ'.length
4
</example>
</tag-desc>

<tag-name id="string_match"><literal>String.prototype.match([<value>regexp</value>])</literal></tag-name>
<tag-desc>
Matches a string against a <literal>regexp</literal>.
<example>
>> 'nginx'.match( /ng/i )
'ng'
</example>
</tag-desc>

<tag-name id="string_padend"><literal>String.prototype.padEnd(<value>length</value>
[, <value>string</value>])</literal></tag-name>
<tag-desc>
Returns a string of a specified <literal>length</literal>
with the pad <literal>string</literal> applied to the end of the specified
string (<link doc="changes.xml" id="njs0.2.3">0.2.3</link>).
<example>
>> '1234'.padEnd(8, 'abcd')
'1234abcd'
</example>
</tag-desc>

<tag-name id="string_padstart"><literal>String.prototype.padStart(<value>length</value>
[, <value>string</value>])</literal></tag-name>
<tag-desc>
Returns a string of a specified <literal>length</literal>
with the pad <literal>string</literal> applied to the start of the specified
string (<link doc="changes.xml" id="njs0.2.3">0.2.3</link>).
<example>
>> '1234'.padStart(8, 'abcd')
'abcd1234'
</example>
</tag-desc>

<tag-name id="string_repeat"><literal>String.prototype.repeat(<value>number</value>)</literal></tag-name>
<tag-desc>
Returns a string
with the specified <literal>number</literal> of copies of the string.
<example>
>> 'abc'.repeat(3)
'abcabcabc'
</example>
</tag-desc>

<tag-name id="string_replace"><literal>String.prototype.replace([<value>regexp</value>|<value>string</value>[,
<value>string</value>|<value>function</value>]])</literal></tag-name>
<tag-desc>
Returns a new string with matches of a pattern
(<literal>string</literal> or a <literal>regexp</literal>)
replaced by a <literal>string</literal> or a <literal>function</literal>.
<example>
>> 'abcdefgh'.replace('d', 1)
'abc1efgh'
</example>
</tag-desc>

<tag-name id="string_search"><literal>String.prototype.search([<value>regexp</value>])</literal></tag-name>
<tag-desc>
Searches for a string using a <literal>regexp</literal>
<example>
>> 'abcdefgh'.search('def')
3
</example>
</tag-desc>

<tag-name id="string_slice"><literal>String.prototype.slice(<value>start</value>[,
<value>end</value>])</literal></tag-name>
<tag-desc>
Returns a new string containing a part of an
original string between <literal>start</literal>
and <literal>end</literal> or
from <literal>start</literal> to the end of the string.
<example>
>> 'abcdefghijklmno'.slice(NaN, 5)
'abcde'
</example>
</tag-desc>

<tag-name id="string_split"><literal>String.prototype.split(([<value>string</value>|<value>regexp</value>[,
<value>limit</value>]]))</literal></tag-name>
<tag-desc>
Returns match of a string against a <literal>regexp</literal>.
The optional <literal>limit</literal> parameter is an integer that specifies
a limit on the number of splits to be found.
<example>
>> 'abc'.split('')
[
 'a',
 'b',
 'c'
]
</example>
</tag-desc>

<tag-name id="string_startswith"><literal>String.prototype.startsWith(<value>searchString</value>[,
<value>position</value>])</literal></tag-name>
<tag-desc>
Returns <literal>true</literal> if a string begins with the characters
of a specified string, otherwise <literal>false</literal>.
The optional <literal>position</literal> parameter is the position
in this string at which to begin search for <literal>searchString</literal>.
Default value is 0.
<example>
>> 'abc'.startsWith('abc')
true
> 'aabc'.startsWith('abc')
false
</example>
</tag-desc>

<tag-name id="string_substr"><literal>String.prototype.substr(<value>start</value>[,
<value>length</value>])</literal></tag-name>
<tag-desc>
Returns the part of the string of the specified <literal>length</literal>
from <literal>start</literal>
or from <literal>start</literal> to the end of the string.
<example>
>>  'abcdefghijklmno'.substr(3, 5)
'defgh'
</example>
</tag-desc>

<tag-name id="string_substring"><literal>String.prototype.substring(<value>start</value>[,
<value>end</value>])</literal></tag-name>
<tag-desc>
Returns the part of the string between
<literal>start</literal> and <literal>end</literal> or
from <literal>start</literal> to the end of the string.
<example>
>> 'abcdefghijklmno'.substring(3, 5)
'de'
</example>
</tag-desc>

<tag-name id="string_tobytes"><literal>String.prototype.toBytes(start[,
end])</literal></tag-name>
<tag-desc>
(njs specific) Serializes a Unicode string to a byte string.
Returns <literal>null</literal> if a character larger than 255 is
found in the string.
</tag-desc>

<tag-name id="string_tolowercase"><literal>String.prototype.toLowerCase()</literal></tag-name>
<tag-desc>
Converts a string to lower case.
The method supports only simple Unicode folding.
<example>
>> 'ΑΒΓΔ'.toLowerCase()
'αβγδ'
</example>
</tag-desc>

<tag-name><literal>String.prototype.toString([<value>encoding</value>])</literal></tag-name>
<tag-desc>
<para>
If no <literal>encoding</literal> is specified,
returns a specified Unicode string or byte string as in ECMAScript.
</para>

<para>
(njs specific) If <literal>encoding</literal> is specified,
encodes a <link id="string_tobytes">byte string</link> to
<literal>hex</literal>,
<literal>base64</literal>, or
<literal>base64url</literal>.
</para>
<example>
>>  'αβγδ'.toUTF8().toString('base64url')
'zrHOss6zzrQ'
</example>
</tag-desc>

<tag-name id="string_touppercase"><literal>String.prototype.toUpperCase()</literal></tag-name>
<tag-desc>
Converts a string to upper case.
The method supports only simple Unicode folding.
<example>
>> 'αβγδ'.toUpperCase()
'ΑΒΓΔ'
</example>
</tag-desc>

<tag-name id="string_toutf8"><literal>String.prototype.toUTF8(<value>start</value>[,
<value>end</value>])</literal></tag-name>
<tag-desc>
(njs specific) Serializes a Unicode string
to a byte string using UTF8 encoding.
<example>
>> 'αβγδ'.toUTF8().length
8
>> 'αβγδ'.length
4
</example>
</tag-desc>

<tag-name id="string_trim"><literal>String.prototype.trim()</literal></tag-name>
<tag-desc>
Removes whitespaces from both ends of a string.
<example>
>> '   abc  '.trim()
'abc'
</example>
</tag-desc>

<tag-name id="string_trimend"><literal>String.prototype.trimEnd()</literal></tag-name>
<tag-desc>
Removes whitespaces from the end of a string
(<link doc="changes.xml" id="njs0.3.4">0.3.4</link>).
<example>
>> '   abc  '.trimEnd()
'   abc'
</example>
</tag-desc>

<tag-name id="string_trimstart"><literal>String.prototype.trimStart()</literal></tag-name>
<tag-desc>
Removes whitespaces from the beginning of a string
(<link doc="changes.xml" id="njs0.3.4">0.3.4</link>).
<example>
>> '   abc  '.trimStart()
'abc  '
</example>
</tag-desc>

<tag-name id="encodeuri"><literal>encodeURI(<value>URI</value>)</literal></tag-name>
<tag-desc>
Encodes a URI by replacing each instance of certain characters
by one, two, three, or four escape sequences
representing the UTF-8 encoding of the character
<example>
>> encodeURI('012αβγδ')
'012%CE%B1%CE%B2%CE%B3%CE%B4'
</example>
</tag-desc>

<tag-name id="encodeuricomponent"><literal>encodeURIComponent(<value>encodedURIString</value>)</literal></tag-name>
<tag-desc>
Encodes a URI by replacing each instance of certain characters
by one, two, three, or four escape sequences
representing the UTF-8 encoding of the character.
<example>
>> encodeURIComponent('[@?=')
'%5B%40%3F%3D'
</example>
</tag-desc>

<tag-name id="decodeuri"><literal>decodeURI(<value>encodedURI</value>)</literal></tag-name>
<tag-desc>
Decodes a previously <link id="encodeuri">encoded</link> URI.
<example>
>> decodeURI('012%CE%B1%CE%B2%CE%B3%CE%B4')
'012αβγδ'
</example>
</tag-desc>

<tag-name id="decodeuricomponent"><literal>decodeURIComponent(<value>decodedURIString</value>)</literal></tag-name>
<tag-desc>
Decodes an encoded component of a previously encoded URI.
<example>
>> decodeURIComponent('%5B%40%3F%3D')
'[@?='
</example>
</tag-desc>

</list>
</para>

</section>


<section id="core_typedarray" name="TypedArray">

<para>
<literal>TypedArray</literal> is a number of different global properties
whose values are typed array constructors for specific element types.
<list type="tag">

<tag-name id="array_sort"><literal>TypedArray.prototype.sort()</literal></tag-name>
<tag-desc>
sorts the elements of a typed array numerically
and returns the updated typed array
(<link doc="changes.xml" id="njs0.4.2">0.4.2</link>).
</tag-desc>
</list>
</para>

</section>


<section id="core_json" name="JSON">

<para>
The <literal>JSON</literal> object (ES 5.1) provides functions
to convert njs values to and from JSON format.
<list type="tag">

<tag-name id="core_json_parse"><literal>JSON.parse(<value>string</value>[,
<value>reviver</value>])</literal></tag-name>
<tag-desc>
Converts a <literal>string</literal> that represents JSON data
into an njs object (<literal>{...}</literal>) or
array (<literal>[...]</literal>).
The optional <literal>reviver</literal> parameter is a function (key, value)
that will be called for each (key,value) pair and can transform the value.
</tag-desc>

<tag-name id="core_json_stringify"><literal>JSON.stringify(<value>value</value>[,
<value>replacer</value>] [, <value>space</value>])</literal></tag-name>
<tag-desc>
Converts an njs object back to JSON.
The obligatory <literal>value</literal> parameter is generally a JSON
<literal>object</literal> or <literal>array</literal> that will be converted.
If the value has a <literal>toJSON()</literal> method,
it defines how the object will be serialized.
The optional <literal>replacer</literal> parameter is
a <literal>function</literal> or <literal>array</literal>
that transforms results.
The optional <literal>space</literal> parameter is
a <literal>string</literal> or <literal>number</literal>.
If it is a <literal>number</literal>,
it indicates the number of white spaces placed before a result
(no more than 10).
If it is a <literal>string</literal>,
it is used as a white space (or first 10 characters of it).
If omitted or is <literal>null</literal>, no white space is used.
</tag-desc>
</list>
</para>

<para>
<example>
>> var json = JSON.parse('{"a":1, "b":true}')
>> json.a
1

>> JSON.stringify(json)
'{"a":1,"b":true}'

>> JSON.stringify({ x: [10, undefined, function(){}] })
'{"x":[10,null,null]}'

>> JSON.stringify({"a":1, "toJSON": function() {return "xxx"}})
'"xxx"'

# Example with function replacer

>> function replacer(key, value) {return (typeof value === 'string') ? undefined : value}
>>JSON.stringify({a:1, b:"b", c:true}, replacer)
'{"a":1,"c":true}'
</example>
</para>

</section>


<section id="crypto" name="Crypto">

<para>
The Crypto module provides cryptographic functionality support.
The Crypto module object is returned by <literal>require('crypto')</literal>.
</para>

<para>
<list type="tag">

<tag-name id="crypto_createhash"><literal>crypto.createHash(<value>algorithm</value>)</literal></tag-name>
<tag-desc>
Creates and returns a <link id="crypto_hash">Hash</link> object
that can be used to generate hash digests
using the given <value>algorithm</value>.
The algorithm can be
<literal>md5</literal>,
<literal>sha1</literal>, and
<literal>sha256</literal>.
</tag-desc>

<tag-name id="crypto_createhmac"><literal>crypto.createHmac(<value>algorithm</value>,
<value>secret key</value>)</literal></tag-name>
<tag-desc>
Creates and returns an <link id="crypto_hmac">HMAC</link> object
that uses the given <value>algorithm</value> and <value>secret key</value>.
The algorithm can be
<literal>md5</literal>,
<literal>sha1</literal>, and
<literal>sha256</literal>.
</tag-desc>

</list>
</para>


<section id="crypto_hash" name="Hash">

<para>
<list type="tag">

<tag-name><literal>hash.update(<value>data</value>)</literal></tag-name>
<tag-desc>
Updates the hash content with the given <value>data</value>.
</tag-desc>

<tag-name><literal>hash.digest([<value>encoding</value>])</literal></tag-name>
<tag-desc>
Calculates the digest of all of the data passed using
<literal>hash.update()</literal>.
The encoding can be
<literal>hex</literal>,
<literal>base64</literal>, and
<literal>base64url</literal>.
If encoding is not provided, a byte string is returned.
</tag-desc>

</list>
</para>

<para>
<example>
>> var cr = require('crypto')
undefined

>> cr.createHash('sha1').update('A').update('B').digest('base64url')
'BtlFlCqiamG-GMPiK_GbvKjdK10'
</example>
</para>

</section>


<section id="crypto_hmac" name="HMAC">

<para>
<list type="tag">

<tag-name><literal>hmac.update(<value>data</value>)</literal></tag-name>
<tag-desc>
Updates the HMAC content with the given <value>data</value>.
</tag-desc>

<tag-name><literal>hmac.digest([<value>encoding</value>])</literal></tag-name>
<tag-desc>
Calculates the HMAC digest of all of the data passed using
<literal>hmac.update()</literal>.
The encoding can be
<literal>hex</literal>,
<literal>base64</literal>, and
<literal>base64url</literal>.
If encoding is not provided, a byte string is returned.
</tag-desc>
</list>
</para>

<para>
<example>
>> var cr = require('crypto')
undefined

>> cr.createHmac('sha1', 'secret.key').update('AB').digest('base64url')
'Oglm93xn23_MkiaEq_e9u8zk374'
</example>
</para>

</section>

</section>

<section id="njs_api_timers" name="Timers">

<para>

<list type="tag">

<tag-name id="cleartimeout"><literal>clearTimeout(<value>timeout</value>)</literal></tag-name>
<tag-desc>
Cancels a <literal>timeout</literal> object
created by <link id="settimeout">setTimeout()</link>.
</tag-desc>

<tag-name id="settimeout"><literal>setTimeout(<value>function</value>,
<value>ms</value>[, <value>arg1</value>, <value>argN</value>])</literal></tag-name>
<tag-desc>
Calls a <literal>function</literal>
after a specified number of <literal>milliseconds</literal>.
One or more optional <literal>arguments</literal>
can be passed to the specified function.
Returns a <literal>timeout</literal> object.
<example>
function handler(v)
{
    // ...
}

t = setTimeout(handler, 12);

// ...

clearTimeout(t);
</example>
</tag-desc>

</list>
</para>

</section>


<section id="njs_api_fs" name="File System">

<para>
The File System module provides operations with files.
</para>

<para>
The module object is returned by <literal>require('fs')</literal>.
Since <link doc="changes.xml" id="njs0.3.9">0.3.9</link>,
promissified versions of file system methods are available through
<literal>require('fs').promises</literal> object:
<example>
> var fs = require('fs').promises;
undefined
> fs.readFile("/file/path").then((data)=>console.log(data))
&lt;file data&gt;
</example>
<list type="tag">

<tag-name id="fs_accesssync"><literal>accessSync(<value>path</value>[,
<value>mode</value>])</literal></tag-name>
<tag-desc>
Synchronously tests permissions for a file or directory
specified in the <literal>path</literal>
(<link doc="changes.xml" id="njs0.3.9">0.3.9</link>).
If the check fails, an error will be returned,
otherwise, the method will return undefined.
<list type="tag">

<tag-name><literal>mode</literal></tag-name>
<tag-desc>
by default is <link id="access_const"><literal>fs.constants.F_OK</literal></link>.
The mode argument is an optional integer
that specifies the accessibility checks to be performed.
<example>
try {
    fs.accessSync('/file/path', fs.constants.R_OK | fs.constants.W_OK);
    console.log('has access');
} catch (e) {
    console.log('no access');)
}
</example>
</tag-desc>

</list>
</tag-desc>

<tag-name id="appendfilesync"><literal>appendFileSync(<value>filename</value>,
<value>data</value>[, <value>options</value>])</literal></tag-name>
<tag-desc>
Synchronously appends specified <literal>data</literal>
to a file with provided <literal>filename</literal>.
If the file does not exist, it will be created.
The <literal>options</literal> parameter is expected to be
an object with the following keys:
<list type="tag">

<tag-name><literal>mode</literal></tag-name>
<tag-desc>
mode option, by default is <literal>0o666</literal>
</tag-desc>

<tag-name><literal>flag</literal></tag-name>
<tag-desc>
file system <link id="njs_api_fs_flags">flag</link>,
by default is <literal>a</literal>
</tag-desc>

</list>
</tag-desc>

<tag-name id="fs_mkdirsync"><literal>mkdirSync(<value>path</value>[,
<value>options</value>])</literal></tag-name>
<tag-desc>
Synchronously creates a directory at the specified <literal>path</literal>
(<link doc="changes.xml" id="njs0.4.2">0.4.2</link>).
The <literal>options</literal> parameter is expected to be an
<literal>integer</literal> that specifies
the <link id="fs_mkdirsync_mode">mode</link>,
or an object with the following keys:
<list type="tag">

<tag-name id="fs_mkdirsync_mode"><literal>mode</literal></tag-name>
<tag-desc>
mode option, by default is <literal>0o777</literal>.
</tag-desc>

</list>
</tag-desc>

<tag-name id="fs_readdirsync"><literal>readdirSync(<value>path</value>[,
<value>options</value>])</literal></tag-name>
<tag-desc>
Synchronously reads the contents of a directory
at the specified <literal>path</literal>
(<link doc="changes.xml" id="njs0.4.2">0.4.2</link>).
The <literal>options</literal> parameter is expected to be
a string that specifies <link id="fs_readdirsync_encoding">encoding</link>
or an object with the following keys:
<list type="tag">

<tag-name id="fs_readdirsync_encoding"><literal>encoding</literal></tag-name>
<tag-desc>
encoding, by default is not specified.
The encoding can be <literal>utf8</literal>.
</tag-desc>

<tag-name id="fs_readdirsync_withfiletypes"><literal>withFileTypes</literal></tag-name>
<tag-desc>
if set to <literal>true</literal>, the files array will contain
<link id="fs_dirent"><literal>fs.Dirent</literal></link> objects,
by default is <literal>false</literal>.
</tag-desc>

</list>
</tag-desc>

<tag-name id="readfilesync"><literal>readFileSync(<value>filename</value>[,
<value>options</value>])</literal></tag-name>
<tag-desc>
Synchronously returns the contents of the file
with provided <literal>filename</literal>.
The <literal>options</literal> parameter holds
<literal>string</literal> that specifies encoding.
If not specified, a <link id="string_tobytes">byte string</link> is returned.
If <literal>utf8</literal> encoding is specified, a Unicode string is returned.
Otherwise, <literal>options</literal> is expected to be
an object with the following keys:
<list type="tag">

<tag-name><literal>encoding</literal></tag-name>
<tag-desc>
encoding, by default is not specified.
The encoding can be <literal>utf8</literal>
</tag-desc>

<tag-name><literal>flag</literal></tag-name>
<tag-desc>
file system <link id="njs_api_fs_flags">flag</link>,
by default is <literal>r</literal>
</tag-desc>

</list>
<example>
>> var fs = require('fs')
undefined
>> var file = fs.readFileSync('/file/path.tar.gz')
undefined
>> var gzipped = /^\x1f\x8b/.test(file); gzipped
true
</example>
</tag-desc>

<tag-name id="fs_realpathsync"><literal>realpathSync(<value>path</value>[,
<value>options</value>])</literal></tag-name>
<tag-desc>
Synchronously computes the canonical pathname by resolving
<literal>.</literal>, <literal>..</literal> and symbolic links using
<link url="http://man7.org/linux/man-pages/man3/realpath.3.html">realpath(3)</link>.
The <literal>options</literal> argument can be a string specifying an encoding,
or an object with an encoding property specifying the character encoding
to use for the path passed to the callback
(<link doc="changes.xml" id="njs0.3.9">0.3.9</link>).
</tag-desc>

<tag-name id="fs_renamesync"><literal>renameSync(<value>oldPath</value>,
<value>newPath</value>)</literal></tag-name>
<tag-desc>
Synchronously changes the name or location of a file from
<literal>oldPath</literal> to <literal>newPath</literal>
(<link doc="changes.xml" id="njs0.3.4">0.3.4</link>).
<example>
>> var fs = require('fs')
undefined
>> var file = fs.renameSync('hello.txt', 'HelloWorld.txt')
undefined
</example>
</tag-desc>

<tag-name id="fs_rmdirsync"><literal>rmdirSync(<value>path</value>)</literal></tag-name>
<tag-desc>
Synchronously removes a directory at the specified <literal>path</literal>
(<link doc="changes.xml" id="njs0.4.2">0.4.2</link>).
</tag-desc>

<tag-name id="fs_symlinksync"><literal>symlinkSync(<value>target</value>,
<value>path</value>)</literal></tag-name>
<tag-desc>
Synchronously creates the link called <literal>path</literal>
pointing to <literal>target</literal> using
<link url="http://man7.org/linux/man-pages/man2/symlink.2.html">symlink(2)</link>
(<link doc="changes.xml" id="njs0.3.9">0.3.9</link>).
Relative targets are relative to the link’s parent directory.
</tag-desc>

<tag-name id="fs_unlinksync"><literal>unlinkSync(<value>path</value>)</literal></tag-name>
<tag-desc>
Synchronously unlinks a file by <literal>path</literal>
(<link doc="changes.xml" id="njs0.3.9">0.3.9</link>).
</tag-desc>

<tag-name id="writefilesync"><literal>writeFileSync(<value>filename</value>,
<value>data</value>[,
<value>options</value>])</literal></tag-name>
<tag-desc>
Synchronously writes <literal>data</literal> to a file
with provided <literal>filename</literal>.
If the file does not exist, it will be created,
if the file exists, it will be replaced.
The <literal>options</literal> parameter is expected to be
an object with the following keys:
<list type="tag">
<tag-name><literal>mode</literal></tag-name>
<tag-desc>
mode option, by default is <literal>0o666</literal>
</tag-desc>

<tag-name><literal>flag</literal></tag-name>
<tag-desc>
file system <link id="njs_api_fs_flags">flag</link>,
by default is <literal>w</literal>
</tag-desc>

</list>
<example>
>> var fs = require('fs')
undefined
>> var file = fs.writeFileSync('hello.txt', 'Hello world')
undefined
</example>
</tag-desc>

</list>
</para>


<section id="fs_dirent" name="fs.Dirent">

<para>
<literal>fs.Dirent</literal> is a representation of a directory entry&mdash;
a file or a subdirectory.
When
<link id="fs_readdirsync"><literal>readdirSync()</literal></link>
is called with the
<link id="fs_readdirsync_withfiletypes"><literal>withFileTypes</literal></link>
option,
the resulting array contains <literal>fs.Dirent</literal> objects.

<list type= "bullet" compact="no">

<listitem>
<literal>dirent.isBlockDevice()</literal>&mdash;returns
<literal>true</literal> if the <literal>fs.Dirent</literal> object describes
a block device.
</listitem>

<listitem>
<literal>dirent.isCharacterDevice()</literal>&mdash;returns
<literal>true</literal> if the <literal>fs.Dirent</literal> object describes
a character device.
</listitem>

<listitem>
<literal>dirent.isDirectory()</literal>&mdash;returns
<literal>true</literal> if the <literal>fs.Dirent</literal> object describes
a file system directory.
</listitem>

<listitem>
<literal>dirent.isFIFO()</literal>&mdash;returns
<literal>true</literal> if the <literal>fs.Dirent</literal> object describes
a first-in-first-out (FIFO) pipe.
</listitem>

<listitem>
<literal>dirent.isFile()</literal>&mdash;returns
<literal>true</literal> if the <literal>fs.Dirent</literal> object describes
a regular file.
</listitem>

<listitem>
<literal>dirent.isSocket()</literal>&mdash;returns
<literal>true</literal> if the <literal>fs.Dirent</literal> object describes
a socket.
</listitem>

<listitem>
<literal>dirent.isSymbolicLink()</literal>&mdash;returns
<literal>true</literal> if the <literal>fs.Dirent</literal> object describes
a symbolic link.
</listitem>

<listitem>
<literal>dirent.name</literal>&mdash;
the name of the file <literal>fs.Dirent</literal> object refers to.
</listitem>

</list>
</para>

</section>


<section id="access_const" name="File Access Constants">

<para>
The <link id="fs_accesssync"><literal>access()</literal></link> method
can accept the following flags.
These flags are exported by <literal>fs.constants</literal>:

<list type= "bullet" compact="no">

<listitem>
<literal>F_OK</literal>&mdash;indicates that the file
is visible to the calling process,
used by default if no mode is specified
</listitem>

<listitem>
<literal>R_OK</literal>&mdash;indicates that the file can be
read by the calling process
</listitem>

<listitem>
<literal>W_OK</literal>&mdash;indicates that the file can be
written by the calling process
</listitem>

<listitem>
<literal>X_OK</literal>&mdash;indicates that the file can be
executed by the calling process
</listitem>

</list>
</para>

</section>


<section id="njs_api_fs_flags" name="File System Flags">

<para>
The <literal>flag</literal> option can accept the following values:

<list type= "bullet" compact="no">

<listitem>
<literal>a</literal>&mdash;open a file for appending.
The file is created if it does not exist
</listitem>

<listitem>
<literal>ax</literal>&mdash;the same as <literal>a</literal>
but fails if the file already exists
</listitem>

<listitem>
<literal>a+</literal>&mdash;open a file for reading and appending.
If the file does not exist, it will be created
</listitem>

<listitem>
<literal>ax+</literal>&mdash;the same as  <literal>a+</literal>
but fails if the file already exists
</listitem>

<listitem>
<literal>as</literal>&mdash;open a file for appending in synchronous mode.
If the file does not exist, it will be created
</listitem>

<listitem>
<literal>as+</literal>&mdash;open a file for reading and appending
in synchronous mode.
If the file does not exist, it will be created
</listitem>

<listitem>
<literal>r</literal>&mdash;open a file for reading.
An exception occurs if the file does not exist
</listitem>

<listitem>
<literal>r+</literal>&mdash;open a file for reading and writing.
An exception occurs if the file does not exist
</listitem>

<listitem>
<literal>rs+</literal>&mdash;open a file for reading and writing
in synchronous mode.
Instructs the operating system to bypass the local file system cache
</listitem>

<listitem>
<literal>w</literal>&mdash;open a file for writing.
If the file does not exist, it will be created.
If the file exists, it will be replaced
</listitem>

<listitem>
<literal>wx</literal>&mdash;the same as <literal>w</literal>
but fails if the file already exists
</listitem>

<listitem>
<literal>w+</literal>&mdash;open a file for reading and writing.
If the file does not exist, it will be created.
If the file exists, it will be replaced
</listitem>

<listitem>
<literal>wx+</literal>&mdash;the same as <literal>w+</literal>
but fails if the file already exists
</listitem>

</list>
</para>

</section>

</section>

</section>

</article>