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<!doctype html> <html lang="en"> <head> <meta charset="utf-8"> <title>Debugger Node.js v0.10.35 Manual & Documentation</title> <link rel="stylesheet" href="assets/style.css"> <link rel="stylesheet" href="assets/sh.css"> <link rel="canonical" href="http://nodejs.org/api/debugger.html"> <script type="text/javascript" src="//use.typekit.net/mse5tqx.js"></script> <script type="text/javascript">try{Typekit.load();}catch(e){}</script> </head> <body class="alt apidoc int docs" id="docs"> <div id="nav"> <img id="logo" src="assets/logo.svg" alt="node.js"> <ul> <li><a href="http://nodejs.org">Home</a></li> <li><a href="http://nodejs.org/download/">Downloads</a></li> <li class="active"><a href="http://nodejs.org/documentation/">Docs</a></li> <li><a href="http://nodejs.org/community/">Community</a></li> <li><a href="http://nodejs.org/about/">About</a></li> <li><a href="http://jobs.nodejs.org">Jobs</a></li> <li><a href="http://blog.nodejs.org">Blog</a></li> </ul> </div> <div id="content-wrap"> <div id="content" class="clearfix"> <div id="column2" class="interior">  <ul class="docs-nav"> <li><a href="http://nodejs.org/documentation/">About Docs</a></li> <li><a href="http://nodejs.org/documentation/tutorials/">Tutorials</a></li> <li><a href="http://nodejs.org/documentation/contributing/">Contributing</a></li> <li><a href="http://nodejs.org/documentation/localization/">Localization</a></li> <li class="active"><a href="http://nodejs.org/api/">API Docs</a></li> </ul> </div> <div id="column1" class="interior"> <header> <h1>Node.js v0.10.35 Manual & Documentation</h1> <div id="gtoc"> <p> <a href="index.html" name="toc">Index</a> | <a href="all.html">View on single page</a> | <a href="debugger.json">View as JSON</a> </p> </div> <hr> </header> <div id="toc"> <h2>Table of Contents</h2> <ul> <li><a href="#debugger_debugger">Debugger</a><ul> <li><a href="#debugger_watchers">Watchers</a></li> <li><a href="#debugger_commands_reference">Commands reference</a><ul> <li><a href="#debugger_stepping">Stepping</a></li> <li><a href="#debugger_breakpoints">Breakpoints</a></li> <li><a href="#debugger_info">Info</a></li> <li><a href="#debugger_execution_control">Execution control</a></li> <li><a href="#debugger_various">Various</a></li> </ul> </li> <li><a href="#debugger_advanced_usage">Advanced Usage</a></li> </ul> </li> </ul> </div> <div id="apicontent"> <h1>Debugger<span><a class="mark" href="#debugger_debugger" id="debugger_debugger">#</a></span></h1> <pre class="api_stability_3">Stability: 3 - Stable</pre> <p>V8 comes with an extensive debugger which is accessible out-of-process via a simple <a href="http://code.google.com/p/v8/wiki/DebuggerProtocol">TCP protocol</a>. Node has a built-in client for this debugger. To use this, start Node with the <code>debug</code> argument; a prompt will appear: </p> <pre><code>% node debug myscript.js < debugger listening on port 5858 connecting... ok break in /home/indutny/Code/git/indutny/myscript.js:1 1 x = 5; 2 setTimeout(function () { 3 debugger; debug></code></pre> <p>Node's debugger client doesn't support the full range of commands, but simple step and inspection is possible. By putting the statement <code>debugger;</code> into the source code of your script, you will enable a breakpoint. </p> <p>For example, suppose <code>myscript.js</code> looked like this: </p> <pre><code>// myscript.js x = 5; setTimeout(function () { debugger; console.log("world"); }, 1000); console.log("hello");</code></pre> <p>Then once the debugger is run, it will break on line 4. </p> <pre><code>% node debug myscript.js < debugger listening on port 5858 connecting... ok break in /home/indutny/Code/git/indutny/myscript.js:1 1 x = 5; 2 setTimeout(function () { 3 debugger; debug> cont < hello break in /home/indutny/Code/git/indutny/myscript.js:3 1 x = 5; 2 setTimeout(function () { 3 debugger; 4 console.log("world"); 5 }, 1000); debug> next break in /home/indutny/Code/git/indutny/myscript.js:4 2 setTimeout(function () { 3 debugger; 4 console.log("world"); 5 }, 1000); 6 console.log("hello"); debug> repl Press Ctrl + C to leave debug repl > x 5 > 2+2 4 debug> next < world break in /home/indutny/Code/git/indutny/myscript.js:5 3 debugger; 4 console.log("world"); 5 }, 1000); 6 console.log("hello"); 7 debug> quit %</code></pre> <p>The <code>repl</code> command allows you to evaluate code remotely. The <code>next</code> command steps over to the next line. There are a few other commands available and more to come. Type <code>help</code> to see others. </p> <h2>Watchers<span><a class="mark" href="#debugger_watchers" id="debugger_watchers">#</a></span></h2> <p>You can watch expression and variable values while debugging your code. On every breakpoint each expression from the watchers list will be evaluated in the current context and displayed just before the breakpoint's source code listing. </p> <p>To start watching an expression, type <code>watch("my_expression")</code>. <code>watchers</code> prints the active watchers. To remove a watcher, type <code>unwatch("my_expression")</code>. </p> <h2>Commands reference<span><a class="mark" href="#debugger_commands_reference" id="debugger_commands_reference">#</a></span></h2> <h3>Stepping<span><a class="mark" href="#debugger_stepping" id="debugger_stepping">#</a></span></h3> <ul> <li><code>cont</code>, <code>c</code> - Continue execution</li> <li><code>next</code>, <code>n</code> - Step next</li> <li><code>step</code>, <code>s</code> - Step in</li> <li><code>out</code>, <code>o</code> - Step out</li> <li><code>pause</code> - Pause running code (like pause button in Developer Tools)</li> </ul> <h3>Breakpoints<span><a class="mark" href="#debugger_breakpoints" id="debugger_breakpoints">#</a></span></h3> <div class="signature"><ul> <li><code>setBreakpoint()</code>, <code>sb()</code> - Set breakpoint on current line</li> <li><code>setBreakpoint(line)</code>, <code>sb(line)</code> - Set breakpoint on specific line</li> <li><code>setBreakpoint('fn()')</code>, <code>sb(...)</code> - Set breakpoint on a first statement in functions body</li> <li><code>setBreakpoint('script.js', 1)</code>, <code>sb(...)</code> - Set breakpoint on first line of script.js</li> <li><code>clearBreakpoint</code>, <code>cb(...)</code> - Clear breakpoint</li> </div></ul> <p>It is also possible to set a breakpoint in a file (module) that isn't loaded yet: </p> <pre><code>% ./node debug test/fixtures/break-in-module/main.js < debugger listening on port 5858 connecting to port 5858... ok break in test/fixtures/break-in-module/main.js:1 1 var mod = require('./mod.js'); 2 mod.hello(); 3 mod.hello(); debug> setBreakpoint('mod.js', 23) Warning: script 'mod.js' was not loaded yet. 1 var mod = require('./mod.js'); 2 mod.hello(); 3 mod.hello(); debug> c break in test/fixtures/break-in-module/mod.js:23 21 22 exports.hello = function() { 23 return 'hello from module'; 24 }; 25 debug></code></pre> <h3>Info<span><a class="mark" href="#debugger_info" id="debugger_info">#</a></span></h3> <div class="signature"><ul> <li><code>backtrace</code>, <code>bt</code> - Print backtrace of current execution frame</li> <li><code>list(5)</code> - List scripts source code with 5 line context (5 lines before and after)</li> <li><code>watch(expr)</code> - Add expression to watch list</li> <li><code>unwatch(expr)</code> - Remove expression from watch list</li> <li><code>watchers</code> - List all watchers and their values (automatically listed on each breakpoint)</li> <li><code>repl</code> - Open debugger's repl for evaluation in debugging script's context</li> </div></ul> <h3>Execution control<span><a class="mark" href="#debugger_execution_control" id="debugger_execution_control">#</a></span></h3> <div class="signature"><ul> <li><code>run</code> - Run script (automatically runs on debugger's start)</li> <li><code>restart</code> - Restart script</li> <li><code>kill</code> - Kill script</li> </div></ul> <h3>Various<span><a class="mark" href="#debugger_various" id="debugger_various">#</a></span></h3> <div class="signature"><ul> <li><code>scripts</code> - List all loaded scripts</li> <li><code>version</code> - Display v8's version</li> </div></ul> <h2>Advanced Usage<span><a class="mark" href="#debugger_advanced_usage" id="debugger_advanced_usage">#</a></span></h2> <p>The V8 debugger can be enabled and accessed either by starting Node with the <code>--debug</code> command-line flag or by signaling an existing Node process with <code>SIGUSR1</code>. </p> <p>Once a process has been set in debug mode with this it can be connected to with the node debugger. Either connect to the <code>pid</code> or the URI to the debugger. The syntax is: </p> <ul> <li><code>node debug -p <pid></code> - Connects to the process via the <code>pid</code></li> <li><code>node debug <URI></code> - Connects to the process via the URI such as localhost:5858</li> </ul> </div> </div> </div> </div> <div id="footer"> <div class="foot-1"> <a href="http://www.joyent.com"><h5>The Node.js Project is Sponsored by</h5> <img src="assets/joyent-footer.svg" width="200"> <p class="tag">Production Node +<br>High Performance Infrastructure</p></a> <a href="https://my.joyent.com/landing/signup/701800000015696" class="button getstarted">Get Started</a> </div> <div class="foot-2"> <div class="foot-nav"> <ul> <li><a href="http://nodejs.org/download/">Downloads</a></li> </ul> <ul> <li><a href="http://nodejs.org/documentation/">Documentation</a></li> <li><a href="http://nodejs.org/api/">API Docs</a></li> <li><a href="http://nodejs.org/documentation/tutorials/">Tutorials</a></li> <li><a href="http://nodejs.org/documentation/localization/">Localization</a></li> </ul> <ul> <li><a href="http://nodejs.org/community/">Community</a></li> <li><a href="https://github.com/joyent/node/issues">Github Issues</a></li> <li><a href="http://groups.google.com/group/nodejs">Mailing List</a></li> <li><a href="http://webchat.freenode.net/?channels=node.js">IRC</a></li> <li><a href="https://twitter.com/nodejs">Twitter</a></li> </ul> <ul> <li><a href="http://nodejs.org/about/">About</a></li> <li><a href="http://nodejs.org/about/organization/">Organization</a></li> <li><a href="http://nodejs.org/about/core-team/">Core Team</a></li> <li><a href="http://nodejs.org/about/resources/">Resources</a></li> </ul> <ul> <li><a href="http://blog.nodejs.org">Blog</a></li> </ul> </div> <p class="copyright">Copyright 2014 <a href="http://joyent.com/">Joyent, Inc</a>, Node.js is a <a href="https://nodejs.org/images/trademark-policy.pdf">trademark</a> of Joyent, Inc. <a href="https://raw.github.com/joyent/node/v0.10.35/LICENSE">View license</a>.</p> </div> </div> <script src="/sh_main.js"></script> <script src="/sh_javascript.min.js"></script> <script>highlight(undefined, undefined, 'pre');</script> <script> window._gaq = [['_setAccount', 'UA-10874194-2'], ['_trackPageview']]; (function(d, t) { var g = d.createElement(t), s = d.getElementsByTagName(t)[0]; g.src = '//www.google-analytics.com/ga.js'; s.parentNode.insertBefore(g, s); }(document, 'script')); </script> </body> </html>