{
  "source": "doc/api/util.markdown",
  "modules": [
    {
      "textRaw": "util",
      "name": "util",
      "stability": 5,
      "stabilityText": "Locked",
      "desc": "<p>These functions are in the module <code>&#39;util&#39;</code>. Use <code>require(&#39;util&#39;)</code> to\naccess them.\n\n</p>\n<p>The <code>util</code> module is primarily designed to support the needs of Node&#39;s\ninternal APIs.  Many of these utilities are useful for your own\nprograms.  If you find that these functions are lacking for your\npurposes, however, you are encouraged to write your own utilities.  We\nare not interested in any future additions to the <code>util</code> module that\nare unnecessary for Node&#39;s internal functionality.\n\n</p>\n",
      "methods": [
        {
          "textRaw": "util.debuglog(section)",
          "type": "method",
          "name": "debuglog",
          "signatures": [
            {
              "return": {
                "textRaw": "Returns: {Function} The logging function ",
                "name": "return",
                "type": "Function",
                "desc": "The logging function"
              },
              "params": [
                {
                  "textRaw": "`section` {String} The section of the program to be debugged ",
                  "name": "section",
                  "type": "String",
                  "desc": "The section of the program to be debugged"
                }
              ]
            },
            {
              "params": [
                {
                  "name": "section"
                }
              ]
            }
          ],
          "desc": "<p>This is used to create a function which conditionally writes to stderr\nbased on the existence of a <code>NODE_DEBUG</code> environment variable.  If the\n<code>section</code> name appears in that environment variable, then the returned\nfunction will be similar to <code>console.error()</code>.  If not, then the\nreturned function is a no-op.\n\n</p>\n<p>For example:\n\n</p>\n<pre><code class=\"javascript\">var debuglog = util.debuglog(&#39;foo&#39;);\n\nvar bar = 123;\ndebuglog(&#39;hello from foo [%d]&#39;, bar);</code></pre>\n<p>If this program is run with <code>NODE_DEBUG=foo</code> in the environment, then\nit will output something like:\n\n</p>\n<pre><code>FOO 3245: hello from foo [123]</code></pre>\n<p>where <code>3245</code> is the process id.  If it is not run with that\nenvironment variable set, then it will not print anything.\n\n</p>\n<p>You may separate multiple <code>NODE_DEBUG</code> environment variables with a\ncomma.  For example, <code>NODE_DEBUG=fs,net,tls</code>.\n\n</p>\n"
        },
        {
          "textRaw": "util.format(format, [...])",
          "type": "method",
          "name": "format",
          "desc": "<p>Returns a formatted string using the first argument as a <code>printf</code>-like format.\n\n</p>\n<p>The first argument is a string that contains zero or more <em>placeholders</em>.\nEach placeholder is replaced with the converted value from its corresponding\nargument. Supported placeholders are:\n\n</p>\n<ul>\n<li><code>%s</code> - String.</li>\n<li><code>%d</code> - Number (both integer and float).</li>\n<li><code>%j</code> - JSON.  Replaced with the string <code>&#39;[Circular]&#39;</code> if the argument<pre><code>   contains circular references.</code></pre>\n</li>\n<li><code>%</code> - single percent sign (<code>&#39;%&#39;</code>). This does not consume an argument.</li>\n</ul>\n<p>If the placeholder does not have a corresponding argument, the placeholder is\nnot replaced.\n\n</p>\n<pre><code>util.format(&#39;%s:%s&#39;, &#39;foo&#39;); // &#39;foo:%s&#39;</code></pre>\n<p>If there are more arguments than placeholders, the extra arguments are\nconverted to strings with <code>util.inspect()</code> and these strings are concatenated,\ndelimited by a space.\n\n</p>\n<pre><code>util.format(&#39;%s:%s&#39;, &#39;foo&#39;, &#39;bar&#39;, &#39;baz&#39;); // &#39;foo:bar baz&#39;</code></pre>\n<p>If the first argument is not a format string then <code>util.format()</code> returns\na string that is the concatenation of all its arguments separated by spaces.\nEach argument is converted to a string with <code>util.inspect()</code>.\n\n</p>\n<pre><code>util.format(1, 2, 3); // &#39;1 2 3&#39;</code></pre>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "format"
                },
                {
                  "name": "...",
                  "optional": true
                }
              ]
            }
          ]
        },
        {
          "textRaw": "util.log(string)",
          "type": "method",
          "name": "log",
          "desc": "<p>Output with timestamp on <code>stdout</code>.\n\n</p>\n<pre><code>require(&#39;util&#39;).log(&#39;Timestamped message.&#39;);</code></pre>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "string"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "util.inspect(object, [options])",
          "type": "method",
          "name": "inspect",
          "desc": "<p>Return a string representation of <code>object</code>, which is useful for debugging.\n\n</p>\n<p>An optional <em>options</em> object may be passed that alters certain aspects of the\nformatted string:\n\n</p>\n<ul>\n<li><p><code>showHidden</code> - if <code>true</code> then the object&#39;s non-enumerable properties will be\nshown too. Defaults to <code>false</code>.</p>\n</li>\n<li><p><code>depth</code> - tells <code>inspect</code> how many times to recurse while formatting the\nobject. This is useful for inspecting large complicated objects. Defaults to\n<code>2</code>. To make it recurse indefinitely pass <code>null</code>.</p>\n</li>\n<li><p><code>colors</code> - if <code>true</code>, then the output will be styled with ANSI color codes.\nDefaults to <code>false</code>. Colors are customizable, see below.</p>\n</li>\n<li><p><code>customInspect</code> - if <code>false</code>, then custom <code>inspect()</code> functions defined on the\nobjects being inspected won&#39;t be called. Defaults to <code>true</code>.</p>\n</li>\n</ul>\n<p>Example of inspecting all properties of the <code>util</code> object:\n\n</p>\n<pre><code>var util = require(&#39;util&#39;);\n\nconsole.log(util.inspect(util, { showHidden: true, depth: null }));</code></pre>\n",
          "miscs": [
            {
              "textRaw": "Customizing `util.inspect` colors",
              "name": "Customizing `util.inspect` colors",
              "type": "misc",
              "desc": "<p>Color output (if enabled) of <code>util.inspect</code> is customizable globally\nvia <code>util.inspect.styles</code> and <code>util.inspect.colors</code> objects.\n\n</p>\n<p><code>util.inspect.styles</code> is a map assigning each style a color\nfrom <code>util.inspect.colors</code>.\nHighlighted styles and their default values are:\n <em> <code>number</code> (yellow)\n </em> <code>boolean</code> (yellow)\n <em> <code>string</code> (green)\n </em> <code>date</code> (magenta)\n <em> <code>regexp</code> (red)\n </em> <code>null</code> (bold)\n <em> <code>undefined</code> (grey)\n </em> <code>special</code> - only function at this time (cyan)\n * <code>name</code> (intentionally no styling)\n\n</p>\n<p>Predefined color codes are: <code>white</code>, <code>grey</code>, <code>black</code>, <code>blue</code>, <code>cyan</code>, \n<code>green</code>, <code>magenta</code>, <code>red</code> and <code>yellow</code>.\nThere are also <code>bold</code>, <code>italic</code>, <code>underline</code> and <code>inverse</code> codes.\n\n</p>\n"
            },
            {
              "textRaw": "Custom `inspect()` function on Objects",
              "name": "Custom `inspect()` function on Objects",
              "type": "misc",
              "desc": "<p>Objects also may define their own <code>inspect(depth)</code> function which <code>util.inspect()</code>\nwill invoke and use the result of when inspecting the object:\n\n</p>\n<pre><code>var util = require(&#39;util&#39;);\n\nvar obj = { name: &#39;nate&#39; };\nobj.inspect = function(depth) {\n  return &#39;{&#39; + this.name + &#39;}&#39;;\n};\n\nutil.inspect(obj);\n  // &quot;{nate}&quot;</code></pre>\n<p>You may also return another Object entirely, and the returned String will be\nformatted according to the returned Object. This is similar to how\n<code>JSON.stringify()</code> works:\n\n</p>\n<pre><code>var obj = { foo: &#39;this will not show up in the inspect() output&#39; };\nobj.inspect = function(depth) {\n  return { bar: &#39;baz&#39; };\n};\n\nutil.inspect(obj);\n  // &quot;{ bar: &#39;baz&#39; }&quot;</code></pre>\n"
            }
          ],
          "signatures": [
            {
              "params": [
                {
                  "name": "object"
                },
                {
                  "name": "options",
                  "optional": true
                }
              ]
            }
          ]
        },
        {
          "textRaw": "util.isArray(object)",
          "type": "method",
          "name": "isArray",
          "desc": "<p>Returns <code>true</code> if the given &quot;object&quot; is an <code>Array</code>. <code>false</code> otherwise.\n\n</p>\n<pre><code>var util = require(&#39;util&#39;);\n\nutil.isArray([])\n  // true\nutil.isArray(new Array)\n  // true\nutil.isArray({})\n  // false</code></pre>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "object"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "util.isRegExp(object)",
          "type": "method",
          "name": "isRegExp",
          "desc": "<p>Returns <code>true</code> if the given &quot;object&quot; is a <code>RegExp</code>. <code>false</code> otherwise.\n\n</p>\n<pre><code>var util = require(&#39;util&#39;);\n\nutil.isRegExp(/some regexp/)\n  // true\nutil.isRegExp(new RegExp(&#39;another regexp&#39;))\n  // true\nutil.isRegExp({})\n  // false</code></pre>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "object"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "util.isDate(object)",
          "type": "method",
          "name": "isDate",
          "desc": "<p>Returns <code>true</code> if the given &quot;object&quot; is a <code>Date</code>. <code>false</code> otherwise.\n\n</p>\n<pre><code>var util = require(&#39;util&#39;);\n\nutil.isDate(new Date())\n  // true\nutil.isDate(Date())\n  // false (without &#39;new&#39; returns a String)\nutil.isDate({})\n  // false</code></pre>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "object"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "util.isError(object)",
          "type": "method",
          "name": "isError",
          "desc": "<p>Returns <code>true</code> if the given &quot;object&quot; is an <code>Error</code>. <code>false</code> otherwise.\n\n</p>\n<pre><code>var util = require(&#39;util&#39;);\n\nutil.isError(new Error())\n  // true\nutil.isError(new TypeError())\n  // true\nutil.isError({ name: &#39;Error&#39;, message: &#39;an error occurred&#39; })\n  // false</code></pre>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "object"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "util.inherits(constructor, superConstructor)",
          "type": "method",
          "name": "inherits",
          "desc": "<p>Inherit the prototype methods from one\n<a href=\"https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Object/constructor\">constructor</a>\ninto another.  The prototype of <code>constructor</code> will be set to a new\nobject created from <code>superConstructor</code>.\n\n</p>\n<p>As an additional convenience, <code>superConstructor</code> will be accessible\nthrough the <code>constructor.super_</code> property.\n\n</p>\n<pre><code>var util = require(&quot;util&quot;);\nvar events = require(&quot;events&quot;);\n\nfunction MyStream() {\n    events.EventEmitter.call(this);\n}\n\nutil.inherits(MyStream, events.EventEmitter);\n\nMyStream.prototype.write = function(data) {\n    this.emit(&quot;data&quot;, data);\n}\n\nvar stream = new MyStream();\n\nconsole.log(stream instanceof events.EventEmitter); // true\nconsole.log(MyStream.super_ === events.EventEmitter); // true\n\nstream.on(&quot;data&quot;, function(data) {\n    console.log(&#39;Received data: &quot;&#39; + data + &#39;&quot;&#39;);\n})\nstream.write(&quot;It works!&quot;); // Received data: &quot;It works!&quot;</code></pre>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "constructor"
                },
                {
                  "name": "superConstructor"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "util.debug(string)",
          "type": "method",
          "name": "debug",
          "stability": 0,
          "stabilityText": "Deprecated: use console.error() instead.",
          "desc": "<p>Deprecated predecessor of <code>console.error</code>.\n\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "string"
                }
              ]
            }
          ]
        },
        {
          "textRaw": "util.error([...])",
          "type": "method",
          "name": "error",
          "stability": 0,
          "stabilityText": "Deprecated: Use console.error() instead.",
          "desc": "<p>Deprecated predecessor of <code>console.error</code>.\n\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "...",
                  "optional": true
                }
              ]
            }
          ]
        },
        {
          "textRaw": "util.puts([...])",
          "type": "method",
          "name": "puts",
          "stability": 0,
          "stabilityText": "Deprecated: Use console.log() instead.",
          "desc": "<p>Deprecated predecessor of <code>console.log</code>.\n\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "...",
                  "optional": true
                }
              ]
            }
          ]
        },
        {
          "textRaw": "util.print([...])",
          "type": "method",
          "name": "print",
          "stability": 0,
          "stabilityText": "Deprecated: Use `console.log` instead.",
          "desc": "<p>Deprecated predecessor of <code>console.log</code>.\n\n\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "...",
                  "optional": true
                }
              ]
            }
          ]
        },
        {
          "textRaw": "util.pump(readableStream, writableStream, [callback])",
          "type": "method",
          "name": "pump",
          "stability": 0,
          "stabilityText": "Deprecated: Use readableStream.pipe(writableStream)",
          "desc": "<p>Deprecated predecessor of <code>stream.pipe()</code>.\n</p>\n",
          "signatures": [
            {
              "params": [
                {
                  "name": "readableStream"
                },
                {
                  "name": "writableStream"
                },
                {
                  "name": "callback",
                  "optional": true
                }
              ]
            }
          ]
        }
      ],
      "type": "module",
      "displayName": "util"
    }
  ]
}