https://github.com/pmuellr/log-callback-error

logs callback errors in JavaScript functions for mobile browsers
https://github.com/pmuellr/log-callback-error

Last synced: about 1 month ago
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logs callback errors in JavaScript functions for mobile browsers

• Host: GitHub
• URL: https://github.com/pmuellr/log-callback-error
• Owner: pmuellr
• Created: 2011-10-11T13:37:21.000Z (about 13 years ago)
• Default Branch: master
• Last Pushed: 2011-10-11T13:42:45.000Z (about 13 years ago)
• Last Synced: 2024-04-09T21:04:45.425Z (9 months ago)
• Language: CoffeeScript
• Homepage:
• Size: 91.8 KB
• Stars: 7
• Watchers: 3
• Forks: 5
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
log-callback-error

==================

A set of overrides to existing JavaScript functions that take callbacks,

which will log an error if an exception is thrown during the invocation of

the callback.

This is aimed primarily for mobile browser engines.

the problem

-----------

On the desktop today, to track down runtime exceptions that are occurring in

your JavaScript code, it's fairly easy to bring up a "web debugger" like Web

Inspector or FireBug, and have it show you where the error occurred.

For mobile platforms, well, we have a problem, because we don't have robust

JavaScript debug capability available.  In fact, often, you have no idea that

any runtime error occurred at all, besides the sneaking feeling that your

application "just isn't working right".

some help

---------

In lieu of this missing function, there's this library.  It instruments a

number of built-in JavaScript functions which take callbacks, and will run

those callbacks in a try/catch.  It will then report the exception to you via

`console.log()`.  In addition, it will display a little bit of context about

the function invocation that specified the callback, as this may help you

further narrow down the problem.

For instance, if you open the file `test/tests.html` in a browser, and

click on the button `setTimeout`, it will run a `setTimeout()` function with a

callback that causes a runtime exception.  You should then see the following

in the console:

    exception executing callback: TypeError: Cannot set property 'x' of null

        callsite:   setTimeout(callbackWithError, 500)

        stacktrace follows

    TypeError: Cannot set property 'x' of null

        at functionThatThrowsError (http://example.com/log-callback-error/test/tests.js:80:9)

        at callbackWithError (http://example.com/log-callback-error/test/tests.js:74:5)

        at http://example.com/log-callback-error/log-callback-error.js:65:21

Note that you'll only see the stacktrace if your browser supports the `stack`

property on exceptions (at least Opera and V8-enabled browsers; Safari flavors

do not yet support the `stack` property).

The stacktrace is the stack at the time the exception occurred.

The second line of the output, labelled with `callsite`,

is the *context* of the call.  It provides

some information about how the callback was initially registered.  In the case

above, it provides the name of the callback function registered, along with

the timeout millisecond value.

usage

-----

Add the line

    

before any other JavaScript files in your HTML files.

functions overridden

--------------------

The following functions are overridden to provide the exception callback

handling:

    window.setTimeout()

    window.setInterval()

    window.addEventListener()

    Node.prototype.addEventListener()

    XMLHttpRequest.prototype.addEventListener()

The `Node.prototype.addEventListener()` override applies to all DOM nodes,

including `document`.  The `XMLHttpRequest` flavor applies to all XHR

requests.

Specifically note, these are the only things overridden.  Need more?  Fork,

add, push.

It seems likely that the `onblahblah` flavored event properties will never

be supported, because the DOM host objects suck.