Javascript Error Debugger
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Javascript Debugger Online
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Javascript Debugger Tool
ToolsFeedback Get Firefox help Get web development help Join the MDN how to debug javascript in visual studio community Report a content problem Report a bug Search Search Languages 中文 (简体) (zh-CN) Add a debugging in software testing translation Edit Advanced Advanced History Print this article MDN Mozilla Debugging Debugging JavaScript Your Search Results jwhitlock AdamskiFTW leplatrem teoli vladikoff mizandaniel wbamberg Pandark fitzgen DCamp maybe jukbot mnoorenberghe http://www.w3schools.com/js/js_debugging.asp Luke314 cold sun PikadudeNo1 Sheppy harth Kastor Dmose evilpie Aryx int3 madarche zhangpin04 siple007 Neil Johnjbarton BenB Ncmathsadist Kohei kohei.yoshino Debugging JavaScript In This Article Web ConsoleBrowser ConsoleError ConsoleBrowser Debugger (Built-in)Strict code checkingConsole.log in Browser Consoledump()Log.jsm (formerly log4moz)"debugger" keywordScratchpadSee AlsoOriginal Document Information This document is intended to help developers writing JavaScript code in Mozilla, mainly for Mozilla https://developer.mozilla.org/en-US/docs/Mozilla/Debugging/Debugging_JavaScript itself, but it may also be useful for web developers. It should give pointers to tools, aids and tricks which make debugging your code easier. Web Console This is the first place to go when you're debugging a web page; open the Web console using the Web Console option in the Web Developer menu. This shows any JavaScript errors in your app, as well as any logging calls from the console API. Browser Console The Browser Console lets you see all JavaScript errors and logging in the browser, including from Firefox code. To enable it, go to about:config in the url bar and set devtools.chrome.enabled to true, or set the "Enable chrome and add-on debugging" option in the developer tool settings. Activate it through with the menu Tools > Web Developer > Browser Console. You can also start the Browser Console when you launch Firefox, by launching Firefox from the command line and passing --jsconsole as a flag: /path/to/firefox --jsconsole Log to the Browser Console using the standard c
Source Firebug Lite Extensions JavaScript Debugger and Profiler Firebug includes a powerful JavaScript debugger that lets you pause execution at any time and see what each variable looked like at that moment. http://getfirebug.com/javascript If your code is a little sluggish, use the JavaScript profiler to measure performance and find bottlenecks fast. Find scripts easily Many web applications are comprised of quite a number of files, and finding the one you want to debug can be a chore. Firebug's script file chooser sorts and organizes files into very clean list that will help you find any file how to in a snap. You can also type to filter the list. Pause execution on any line Firebug allows you to set breakpoints, which tell the debugger to pause execution when it reaches a specific line. While execution is pause, you can see the value of any variable and inspect objects while time is frozen. To set breakpoints, just click on any line number, and how to debug a red dot will appear to indicate that the breakpoint is set. Click the red dot again to remove the breakpoint. Pause execution, but only if... Breakpoints can be troublesome if you find them breaking too often. Sometimes you only want to pause under very specific conditions. Firebug allows you to set conditional breakpoints, which check an expression that must be true for the breakpoint to pause. To set a conditional breakpoint, just right-click on any line number. A bubble will appear that prompts you to enter a JavaScript expression. You can right-click again at any time to change the expression, or left-click to remove the breakpoint altogether. One step at a time Once the debugger is paused, you can continue execution one line at a time. This allows you to see exactly how variables and objects are effected when a particular line is executed. You can also choose to step execution for more than one line. From the context menu, choose "Run to this Line" to continue execution until it passes through the line you clicked. I break for errors You don't always choose to use the debugger. Sometim