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<!doctype html> <html lang="en"> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width"> <title>REPL | Node.js v8.10.0 Documentation</title> <link rel="stylesheet" href="assets/style.css"> <link rel="stylesheet" href="assets/sh.css"> <link rel="canonical" href="repl.html"> </head> <body class="alt apidoc" id="api-section-repl"> <div id="content" class="clearfix"> <div id="column2" class="interior"> <div id="intro" class="interior"> <a href="/" title="Go back to the home page"> Node.js </a> </div> <ul> <li><a class="nav-documentation" href="documentation.html">About these Docs</a></li> <li><a class="nav-synopsis" href="synopsis.html">Usage & Example</a></li> </ul> <div class="line"></div> <ul> <li><a class="nav-assert" href="assert.html">Assertion Testing</a></li> <li><a class="nav-async_hooks" href="async_hooks.html">Async Hooks</a></li> <li><a class="nav-buffer" href="buffer.html">Buffer</a></li> <li><a class="nav-addons" href="addons.html">C++ 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<div id="column1" data-id="repl" class="interior"> <header> <h1>Node.js v8.10.0 Documentation</h1> <div id="gtoc"> <ul> <li> <a href="index.html" name="toc">Index</a> </li> <li> <a href="all.html">View on single page</a> </li> <li> <a href="repl.json">View as JSON</a> </li> <li class="version-picker"> <a href="#">View another version <span>▼</span></a> <ol class="version-picker"><li><a href="https://nodejs.org/docs/latest-v9.x/api/repl.html">9.x</a></li> <li><a href="https://nodejs.org/docs/latest-v8.x/api/repl.html">8.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v7.x/api/repl.html">7.x</a></li> <li><a href="https://nodejs.org/docs/latest-v6.x/api/repl.html">6.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v5.x/api/repl.html">5.x</a></li> <li><a href="https://nodejs.org/docs/latest-v4.x/api/repl.html">4.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v0.12.x/api/repl.html">0.12.x</a></li> <li><a href="https://nodejs.org/docs/latest-v0.10.x/api/repl.html">0.10.x</a></li></ol> </li> </ul> </div> <hr> </header> <div id="toc"> <h2>Table of Contents</h2> <ul> <li><span class="stability_2"><a href="#repl_repl">REPL</a></span><ul> <li><span class="stability_undefined"><a href="#repl_design_and_features">Design and Features</a></span><ul> <li><span class="stability_undefined"><a href="#repl_commands_and_special_keys">Commands and Special Keys</a></span></li> <li><span class="stability_undefined"><a href="#repl_default_evaluation">Default Evaluation</a></span><ul> <li><span class="stability_undefined"><a href="#repl_javascript_expressions">JavaScript Expressions</a></span></li> <li><span class="stability_undefined"><a href="#repl_global_and_local_scope">Global and Local Scope</a></span></li> <li><span class="stability_undefined"><a href="#repl_accessing_core_node_js_modules">Accessing Core Node.js Modules</a></span></li> <li><span class="stability_undefined"><a href="#repl_assignment_of_the_underscore_variable">Assignment of the <code>_</code> (underscore) variable</a></span></li> </ul> </li> <li><span class="stability_undefined"><a href="#repl_custom_evaluation_functions">Custom Evaluation Functions</a></span><ul> <li><span class="stability_undefined"><a href="#repl_recoverable_errors">Recoverable Errors</a></span></li> </ul> </li> <li><span class="stability_undefined"><a href="#repl_customizing_repl_output">Customizing REPL Output</a></span></li> </ul> </li> <li><span class="stability_undefined"><a href="#repl_class_replserver">Class: REPLServer</a></span><ul> <li><span class="stability_undefined"><a href="#repl_event_exit">Event: 'exit'</a></span></li> <li><span class="stability_undefined"><a href="#repl_event_reset">Event: 'reset'</a></span></li> <li><span class="stability_undefined"><a href="#repl_replserver_definecommand_keyword_cmd">replServer.defineCommand(keyword, cmd)</a></span></li> <li><span class="stability_undefined"><a href="#repl_replserver_displayprompt_preservecursor">replServer.displayPrompt([preserveCursor])</a></span></li> </ul> </li> <li><span class="stability_undefined"><a href="#repl_repl_start_options">repl.start([options])</a></span></li> <li><span class="stability_undefined"><a href="#repl_the_node_js_repl">The Node.js REPL</a></span><ul> <li><span class="stability_undefined"><a href="#repl_environment_variable_options">Environment Variable Options</a></span></li> <li><span class="stability_undefined"><a href="#repl_persistent_history">Persistent History</a></span><ul> <li><span class="stability_0"><a href="#repl_node_repl_history_file">NODE_REPL_HISTORY_FILE</a></span></li> </ul> </li> <li><span class="stability_undefined"><a href="#repl_using_the_node_js_repl_with_advanced_line_editors">Using the Node.js REPL with advanced line-editors</a></span></li> <li><span class="stability_undefined"><a href="#repl_starting_multiple_repl_instances_against_a_single_running_instance">Starting multiple REPL instances against a single running instance</a></span></li> </ul> </li> </ul> </li> </ul> </div> <div id="apicontent"> <h1>REPL<span><a class="mark" href="#repl_repl" id="repl_repl">#</a></span></h1> <!--introduced_in=v0.10.0--> <div class="api_stability api_stability_2"><a href="documentation.html#documentation_stability_index">Stability: 2</a> - Stable</div><p>The <code>repl</code> module provides a Read-Eval-Print-Loop (REPL) implementation that is available both as a standalone program or includible in other applications. It can be accessed using:</p> <pre><code class="lang-js">const repl = require('repl'); </code></pre> <h2>Design and Features<span><a class="mark" href="#repl_design_and_features" id="repl_design_and_features">#</a></span></h2> <p>The <code>repl</code> module exports the <code>repl.REPLServer</code> class. While running, instances of <code>repl.REPLServer</code> will accept individual lines of user input, evaluate those according to a user-defined evaluation function, then output the result. Input and output may be from <code>stdin</code> and <code>stdout</code>, respectively, or may be connected to any Node.js <a href="stream.html">stream</a>.</p> <p>Instances of <code>repl.REPLServer</code> support automatic completion of inputs, simplistic Emacs-style line editing, multi-line inputs, ANSI-styled output, saving and restoring current REPL session state, error recovery, and customizable evaluation functions.</p> <h3>Commands and Special Keys<span><a class="mark" href="#repl_commands_and_special_keys" id="repl_commands_and_special_keys">#</a></span></h3> <p>The following special commands are supported by all REPL instances:</p> <ul> <li><code>.break</code> - When in the process of inputting a multi-line expression, entering the <code>.break</code> command (or pressing the <code><ctrl>-C</code> key combination) will abort further input or processing of that expression.</li> <li><code>.clear</code> - Resets the REPL <code>context</code> to an empty object and clears any multi-line expression currently being input.</li> <li><code>.exit</code> - Close the I/O stream, causing the REPL to exit.</li> <li><code>.help</code> - Show this list of special commands.</li> <li><code>.save</code> - Save the current REPL session to a file: <code>> .save ./file/to/save.js</code></li> <li><code>.load</code> - Load a file into the current REPL session. <code>> .load ./file/to/load.js</code></li> <li><code>.editor</code> - Enter editor mode (<code><ctrl>-D</code> to finish, <code><ctrl>-C</code> to cancel)</li> </ul> <!-- eslint-skip --> <pre><code class="lang-js">> .editor // Entering editor mode (^D to finish, ^C to cancel) function welcome(name) { return `Hello ${name}!`; } welcome('Node.js User'); // ^D 'Hello Node.js User!' > </code></pre> <p>The following key combinations in the REPL have these special effects:</p> <ul> <li><code><ctrl>-C</code> - When pressed once, has the same effect as the <code>.break</code> command. When pressed twice on a blank line, has the same effect as the <code>.exit</code> command.</li> <li><code><ctrl>-D</code> - Has the same effect as the <code>.exit</code> command.</li> <li><code><tab></code> - When pressed on a blank line, displays global and local(scope) variables. When pressed while entering other input, displays relevant autocompletion options.</li> </ul> <h3>Default Evaluation<span><a class="mark" href="#repl_default_evaluation" id="repl_default_evaluation">#</a></span></h3> <p>By default, all instances of <code>repl.REPLServer</code> use an evaluation function that evaluates JavaScript expressions and provides access to Node.js' built-in modules. This default behavior can be overridden by passing in an alternative evaluation function when the <code>repl.REPLServer</code> instance is created.</p> <h4>JavaScript Expressions<span><a class="mark" href="#repl_javascript_expressions" id="repl_javascript_expressions">#</a></span></h4> <p>The default evaluator supports direct evaluation of JavaScript expressions:</p> <!-- eslint-skip --> <pre><code class="lang-js">> 1 + 1 2 > const m = 2 undefined > m + 1 3 </code></pre> <p>Unless otherwise scoped within blocks or functions, variables declared either implicitly or using the <code>const</code>, <code>let</code>, or <code>var</code> keywords are declared at the global scope.</p> <h4>Global and Local Scope<span><a class="mark" href="#repl_global_and_local_scope" id="repl_global_and_local_scope">#</a></span></h4> <p>The default evaluator provides access to any variables that exist in the global scope. It is possible to expose a variable to the REPL explicitly by assigning it to the <code>context</code> object associated with each <code>REPLServer</code>. For example:</p> <pre><code class="lang-js">const repl = require('repl'); const msg = 'message'; repl.start('> ').context.m = msg; </code></pre> <p>Properties in the <code>context</code> object appear as local within the REPL:</p> <!-- eslint-skip --> <pre><code class="lang-js">$ node repl_test.js > m 'message' </code></pre> <p>Context properties are not read-only by default. To specify read-only globals, context properties must be defined using <code>Object.defineProperty()</code>:</p> <pre><code class="lang-js">const repl = require('repl'); const msg = 'message'; const r = repl.start('> '); Object.defineProperty(r.context, 'm', { configurable: false, enumerable: true, value: msg }); </code></pre> <h4>Accessing Core Node.js Modules<span><a class="mark" href="#repl_accessing_core_node_js_modules" id="repl_accessing_core_node_js_modules">#</a></span></h4> <p>The default evaluator will automatically load Node.js core modules into the REPL environment when used. For instance, unless otherwise declared as a global or scoped variable, the input <code>fs</code> will be evaluated on-demand as <code>global.fs = require('fs')</code>.</p> <!-- eslint-skip --> <pre><code class="lang-js">> fs.createReadStream('./some/file'); </code></pre> <h4>Assignment of the <code>_</code> (underscore) variable<span><a class="mark" href="#repl_assignment_of_the_underscore_variable" id="repl_assignment_of_the_underscore_variable">#</a></span></h4> <p>The default evaluator will, by default, assign the result of the most recently evaluated expression to the special variable <code>_</code> (underscore). Explicitly setting <code>_</code> to a value will disable this behavior.</p> <!-- eslint-skip --> <pre><code class="lang-js">> [ 'a', 'b', 'c' ] [ 'a', 'b', 'c' ] > _.length 3 > _ += 1 Expression assignment to _ now disabled. 4 > 1 + 1 2 > _ 4 </code></pre> <h3>Custom Evaluation Functions<span><a class="mark" href="#repl_custom_evaluation_functions" id="repl_custom_evaluation_functions">#</a></span></h3> <p>When a new <code>repl.REPLServer</code> is created, a custom evaluation function may be provided. This can be used, for instance, to implement fully customized REPL applications.</p> <p>The following illustrates a hypothetical example of a REPL that performs translation of text from one language to another:</p> <pre><code class="lang-js">const repl = require('repl'); const { Translator } = require('translator'); const myTranslator = new Translator('en', 'fr'); function myEval(cmd, context, filename, callback) { callback(null, myTranslator.translate(cmd)); } repl.start({ prompt: '> ', eval: myEval }); </code></pre> <h4>Recoverable Errors<span><a class="mark" href="#repl_recoverable_errors" id="repl_recoverable_errors">#</a></span></h4> <p>As a user is typing input into the REPL prompt, pressing the <code><enter></code> key will send the current line of input to the <code>eval</code> function. In order to support multi-line input, the eval function can return an instance of <code>repl.Recoverable</code> to the provided callback function:</p> <pre><code class="lang-js">function myEval(cmd, context, filename, callback) { let result; try { result = vm.runInThisContext(cmd); } catch (e) { if (isRecoverableError(e)) { return callback(new repl.Recoverable(e)); } } callback(null, result); } function isRecoverableError(error) { if (error.name === 'SyntaxError') { return /^(Unexpected end of input|Unexpected token)/.test(error.message); } return false; } </code></pre> <h3>Customizing REPL Output<span><a class="mark" href="#repl_customizing_repl_output" id="repl_customizing_repl_output">#</a></span></h3> <p>By default, <code>repl.REPLServer</code> instances format output using the <a href="util.html#util_util_inspect_object_options"><code>util.inspect()</code></a> method before writing the output to the provided Writable stream (<code>process.stdout</code> by default). The <code>useColors</code> boolean option can be specified at construction to instruct the default writer to use ANSI style codes to colorize the output from the <code>util.inspect()</code> method.</p> <p>It is possible to fully customize the output of a <code>repl.REPLServer</code> instance by passing a new function in using the <code>writer</code> option on construction. The following example, for instance, simply converts any input text to upper case:</p> <pre><code class="lang-js">const repl = require('repl'); const r = repl.start({ prompt: '> ', eval: myEval, writer: myWriter }); function myEval(cmd, context, filename, callback) { callback(null, cmd); } function myWriter(output) { return output.toUpperCase(); } </code></pre> <h2>Class: REPLServer<span><a class="mark" href="#repl_class_replserver" id="repl_class_replserver">#</a></span></h2> <div class="api_metadata"> <span>Added in: v0.1.91</span> </div><p>The <code>repl.REPLServer</code> class inherits from the <a href="readline.html#readline_class_interface"><code>readline.Interface</code></a> class. Instances of <code>repl.REPLServer</code> are created using the <code>repl.start()</code> method and <em>should not</em> be created directly using the JavaScript <code>new</code> keyword.</p> <h3>Event: 'exit'<span><a class="mark" href="#repl_event_exit" id="repl_event_exit">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.7.7</span> </div><p>The <code>'exit'</code> event is emitted when the REPL is exited either by receiving the <code>.exit</code> command as input, the user pressing <code><ctrl>-C</code> twice to signal <code>SIGINT</code>, or by pressing <code><ctrl>-D</code> to signal <code>'end'</code> on the input stream. The listener callback is invoked without any arguments.</p> <pre><code class="lang-js">replServer.on('exit', () => { console.log('Received "exit" event from repl!'); process.exit(); }); </code></pre> <h3>Event: 'reset'<span><a class="mark" href="#repl_event_reset" id="repl_event_reset">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.11.0</span> </div><p>The <code>'reset'</code> event is emitted when the REPL's context is reset. This occurs whenever the <code>.clear</code> command is received as input <em>unless</em> the REPL is using the default evaluator and the <code>repl.REPLServer</code> instance was created with the <code>useGlobal</code> option set to <code>true</code>. The listener callback will be called with a reference to the <code>context</code> object as the only argument.</p> <p>This can be used primarily to re-initialize REPL context to some pre-defined state as illustrated in the following simple example:</p> <pre><code class="lang-js">const repl = require('repl'); function initializeContext(context) { context.m = 'test'; } const r = repl.start({ prompt: '> ' }); initializeContext(r.context); r.on('reset', initializeContext); </code></pre> <p>When this code is executed, the global <code>'m'</code> variable can be modified but then reset to its initial value using the <code>.clear</code> command:</p> <!-- eslint-skip --> <pre><code class="lang-js">$ ./node example.js > m 'test' > m = 1 1 > m 1 > .clear Clearing context... > m 'test' > </code></pre> <h3>replServer.defineCommand(keyword, cmd)<span><a class="mark" href="#repl_replserver_definecommand_keyword_cmd" id="repl_replserver_definecommand_keyword_cmd">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.3.0</span> </div><ul> <li><code>keyword</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The command keyword (<em>without</em> a leading <code>.</code> character).</li> <li><code>cmd</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The function to invoke when the command is processed.</li> </ul> <p>The <code>replServer.defineCommand()</code> method is used to add new <code>.</code>-prefixed commands to the REPL instance. Such commands are invoked by typing a <code>.</code> followed by the <code>keyword</code>. The <code>cmd</code> is either a Function or an object with the following properties:</p> <ul> <li><code>help</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Help text to be displayed when <code>.help</code> is entered (Optional).</li> <li><code>action</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The function to execute, optionally accepting a single string argument.</li> </ul> <p>The following example shows two new commands added to the REPL instance:</p> <pre><code class="lang-js">const repl = require('repl'); const replServer = repl.start({ prompt: '> ' }); replServer.defineCommand('sayhello', { help: 'Say hello', action(name) { this.bufferedCommand = ''; console.log(`Hello, ${name}!`); this.displayPrompt(); } }); replServer.defineCommand('saybye', function saybye() { console.log('Goodbye!'); this.close(); }); </code></pre> <p>The new commands can then be used from within the REPL instance:</p> <pre><code class="lang-txt">> .sayhello Node.js User Hello, Node.js User! > .saybye Goodbye! </code></pre> <h3>replServer.displayPrompt([preserveCursor])<span><a class="mark" href="#repl_replserver_displayprompt_preservecursor" id="repl_replserver_displayprompt_preservecursor">#</a></span></h3> <div class="api_metadata"> <span>Added in: v0.1.91</span> </div><ul> <li><code>preserveCursor</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>The <code>replServer.displayPrompt()</code> method readies the REPL instance for input from the user, printing the configured <code>prompt</code> to a new line in the <code>output</code> and resuming the <code>input</code> to accept new input.</p> <p>When multi-line input is being entered, an ellipsis is printed rather than the 'prompt'.</p> <p>When <code>preserveCursor</code> is <code>true</code>, the cursor placement will not be reset to <code>0</code>.</p> <p>The <code>replServer.displayPrompt</code> method is primarily intended to be called from within the action function for commands registered using the <code>replServer.defineCommand()</code> method.</p> <h2>repl.start([options])<span><a class="mark" href="#repl_repl_start_options" id="repl_repl_start_options">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tr><th>Version</th><th>Changes</th></tr> <tr><td>v5.8.0</td> <td><p>The <code>options</code> parameter is optional now.</p> </td></tr> <tr><td>v0.1.91</td> <td><p><span>Added in: v0.1.91</span></p> </td></tr> </table> </details> </div><ul> <li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a><ul> <li><code>prompt</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The input prompt to display. Defaults to <code>></code> (with a trailing space).</li> <li><code>input</code> <span class="type"><Readable></span> The Readable stream from which REPL input will be read. Defaults to <code>process.stdin</code>.</li> <li><code>output</code> <span class="type"><Writable></span> The Writable stream to which REPL output will be written. Defaults to <code>process.stdout</code>.</li> <li><code>terminal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, specifies that the <code>output</code> should be treated as a TTY terminal, and have ANSI/VT100 escape codes written to it. Defaults to checking the value of the <code>isTTY</code> property on the <code>output</code> stream upon instantiation.</li> <li><code>eval</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The function to be used when evaluating each given line of input. Defaults to an async wrapper for the JavaScript <code>eval()</code> function. An <code>eval</code> function can error with <code>repl.Recoverable</code> to indicate the input was incomplete and prompt for additional lines.</li> <li><code>useColors</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, specifies that the default <code>writer</code> function should include ANSI color styling to REPL output. If a custom <code>writer</code> function is provided then this has no effect. Defaults to the REPL instances <code>terminal</code> value.</li> <li><code>useGlobal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, specifies that the default evaluation function will use the JavaScript <code>global</code> as the context as opposed to creating a new separate context for the REPL instance. The node CLI REPL sets this value to <code>true</code>. Defaults to <code>false</code>.</li> <li><code>ignoreUndefined</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, specifies that the default writer will not output the return value of a command if it evaluates to <code>undefined</code>. Defaults to <code>false</code>.</li> <li><code>writer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The function to invoke to format the output of each command before writing to <code>output</code>. Defaults to <a href="util.html#util_util_inspect_object_options"><code>util.inspect()</code></a>.</li> <li><code>completer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> An optional function used for custom Tab auto completion. See <a href="readline.html#readline_use_of_the_completer_function"><code>readline.InterfaceCompleter</code></a> for an example.</li> <li><code>replMode</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type" class="type"><symbol></a> A flag that specifies whether the default evaluator executes all JavaScript commands in strict mode or default (sloppy) mode. Acceptable values are:<ul> <li><code>repl.REPL_MODE_SLOPPY</code> - evaluates expressions in sloppy mode.</li> <li><code>repl.REPL_MODE_STRICT</code> - evaluates expressions in strict mode. This is equivalent to prefacing every repl statement with <code>'use strict'</code>.</li> <li><code>repl.REPL_MODE_MAGIC</code> - This value is <strong>deprecated</strong>, since enhanced spec compliance in V8 has rendered magic mode unnecessary. It is now equivalent to <code>repl.REPL_MODE_SLOPPY</code> (documented above).</li> </ul> </li> <li><code>breakEvalOnSigint</code> - Stop evaluating the current piece of code when <code>SIGINT</code> is received, i.e. <code>Ctrl+C</code> is pressed. This cannot be used together with a custom <code>eval</code> function. Defaults to <code>false</code>.</li> </ul> </li> </ul> <p>The <code>repl.start()</code> method creates and starts a <code>repl.REPLServer</code> instance.</p> <p>If <code>options</code> is a string, then it specifies the input prompt:</p> <pre><code class="lang-js">const repl = require('repl'); // a Unix style prompt repl.start('$ '); </code></pre> <h2>The Node.js REPL<span><a class="mark" href="#repl_the_node_js_repl" id="repl_the_node_js_repl">#</a></span></h2> <p>Node.js itself uses the <code>repl</code> module to provide its own interactive interface for executing JavaScript. This can be used by executing the Node.js binary without passing any arguments (or by passing the <code>-i</code> argument):</p> <!-- eslint-skip --> <pre><code class="lang-js">$ node > const a = [1, 2, 3]; undefined > a [ 1, 2, 3 ] > a.forEach((v) => { ... console.log(v); ... }); 1 2 3 </code></pre> <h3>Environment Variable Options<span><a class="mark" href="#repl_environment_variable_options" id="repl_environment_variable_options">#</a></span></h3> <p>Various behaviors of the Node.js REPL can be customized using the following environment variables:</p> <ul> <li><code>NODE_REPL_HISTORY</code> - When a valid path is given, persistent REPL history will be saved to the specified file rather than <code>.node_repl_history</code> in the user's home directory. Setting this value to <code>""</code> will disable persistent REPL history. Whitespace will be trimmed from the value.</li> <li><code>NODE_REPL_HISTORY_SIZE</code> - Defaults to <code>1000</code>. Controls how many lines of history will be persisted if history is available. Must be a positive number.</li> <li><code>NODE_REPL_MODE</code> - May be any of <code>sloppy</code>, <code>strict</code>, or <code>magic</code>. Defaults to <code>sloppy</code>, which will allow non-strict mode code to be run. <code>magic</code> is <strong>deprecated</strong> and treated as an alias of <code>sloppy</code>.</li> </ul> <h3>Persistent History<span><a class="mark" href="#repl_persistent_history" id="repl_persistent_history">#</a></span></h3> <p>By default, the Node.js REPL will persist history between <code>node</code> REPL sessions by saving inputs to a <code>.node_repl_history</code> file located in the user's home directory. This can be disabled by setting the environment variable <code>NODE_REPL_HISTORY=""</code>.</p> <h4>NODE_REPL_HISTORY_FILE<span><a class="mark" href="#repl_node_repl_history_file" id="repl_node_repl_history_file">#</a></span></h4> <div class="api_metadata"> <span>Added in: v2.0.0</span><span>Deprecated since: v3.0.0</span> </div><div class="api_stability api_stability_0"><a href="documentation.html#documentation_stability_index">Stability: 0</a> - Deprecated: Use <code>NODE_REPL_HISTORY</code> instead.</div><p>Previously in Node.js/io.js v2.x, REPL history was controlled by using a <code>NODE_REPL_HISTORY_FILE</code> environment variable, and the history was saved in JSON format. This variable has now been deprecated, and the old JSON REPL history file will be automatically converted to a simplified plain text format. This new file will be saved to either the user's home directory, or a directory defined by the <code>NODE_REPL_HISTORY</code> variable, as documented in the <a href="#repl_environment_variable_options">Environment Variable Options</a>.</p> <h3>Using the Node.js REPL with advanced line-editors<span><a class="mark" href="#repl_using_the_node_js_repl_with_advanced_line_editors" id="repl_using_the_node_js_repl_with_advanced_line_editors">#</a></span></h3> <p>For advanced line-editors, start Node.js with the environment variable <code>NODE_NO_READLINE=1</code>. This will start the main and debugger REPL in canonical terminal settings, which will allow use with <code>rlwrap</code>.</p> <p>For example, the following can be added to a <code>.bashrc</code> file:</p> <pre><code class="lang-text">alias node="env NODE_NO_READLINE=1 rlwrap node" </code></pre> <h3>Starting multiple REPL instances against a single running instance<span><a class="mark" href="#repl_starting_multiple_repl_instances_against_a_single_running_instance" id="repl_starting_multiple_repl_instances_against_a_single_running_instance">#</a></span></h3> <p>It is possible to create and run multiple REPL instances against a single running instance of Node.js that share a single <code>global</code> object but have separate I/O interfaces.</p> <p>The following example, for instance, provides separate REPLs on <code>stdin</code>, a Unix socket, and a TCP socket:</p> <pre><code class="lang-js">const net = require('net'); const repl = require('repl'); let connections = 0; repl.start({ prompt: 'Node.js via stdin> ', input: process.stdin, output: process.stdout }); net.createServer((socket) => { connections += 1; repl.start({ prompt: 'Node.js via Unix socket> ', input: socket, output: socket }).on('exit', () => { socket.end(); }); }).listen('/tmp/node-repl-sock'); net.createServer((socket) => { connections += 1; repl.start({ prompt: 'Node.js via TCP socket> ', input: socket, output: socket }).on('exit', () => { socket.end(); }); }).listen(5001); </code></pre> <p>Running this application from the command line will start a REPL on stdin. Other REPL clients may connect through the Unix socket or TCP socket. <code>telnet</code>, for instance, is useful for connecting to TCP sockets, while <code>socat</code> can be used to connect to both Unix and TCP sockets.</p> <p>By starting a REPL from a Unix socket-based server instead of stdin, it is possible to connect to a long-running Node.js process without restarting it.</p> <p>For an example of running a "full-featured" (<code>terminal</code>) REPL over a <code>net.Server</code> and <code>net.Socket</code> instance, see: <a href="https://gist.github.com/2209310">https://gist.github.com/2209310</a></p> <p>For an example of running a REPL instance over <a href="https://curl.haxx.se/docs/manpage.html">curl(1)</a>, see: <a href="https://gist.github.com/2053342">https://gist.github.com/2053342</a></p> </div> </div> </div> <script src="assets/sh_main.js"></script> <script src="assets/sh_javascript.min.js"></script> <script>highlight(undefined, undefined, 'pre');</script> <!-- __TRACKING__ --> </body> </html>