223686 - Support XUL-based assertions and warnings?

Status: RESOLVED WONTFIX

(Core :: XUL, enhancement)

Description

[Alex Vincent [:WeirdAl]]

In C++ code, developers have the power to set assertions and warnings for bugs
in the design as they see fit.  I'd like to have the same power from JavaScript,
without an onerous requirement.

I would suggest the following for chrome://global/content/ecma_assert.js:

function assert(assertString, thisObj) {
  var throwException = arguments.length > 2 ? arguments[2] : false;
  var argsObj = arguments.length > 3 ? arguments[3] : {}
  var argsString = "";
  for (var property in argsObj) {
    argsString += ("var " + property + " = " + argsObj[property] +";\n");
  }
  var func = new Function(argsString + "return (" + assertString + ");");
  dump (func);
  var mustBeTrue = false;
  try {
    mustBeTrue = func.apply(thisObj);
  }
  catch(e) {
    dump(e + "\n" + e.stack);
  }
  
  try {
    if (!mustBeTrue) {
     throw new Error("ECMAScript assertion failed:  (" + assertString + ")");
    }
  }
  catch(e) {
    if (throwException) {
      throw new Error(e.message + " stack:\n" + e.stack);
    } else {
      dump ("Warning: " + e.message + " stack:\n" + e.stack);
    }
  }
}

Usage:  From whatever JS function wishes to make a warning check, call
assert(assertString, this).  If you want an assertion to actually go out as an
exception, assert(assertString, this, true).  If you want to pass arguments,
pass them as named string properties of an object:

assert("x.ownerDocument == document", this, false, {x: "this.foo"});

I can generate a patch very quickly if this is a desired feature.  As I do not
know whether XUL application developers would want it, I'm filing this as an
RFE.  Comments on making the assert() function better are also welcome.

Comment 1

[Alex Vincent [:WeirdAl]]

Hm, a couple things I need to think about:

(1) Optimized builds shouldn't see these assertions.  A blank assert() script
should be provided for those.  Maybe some Perl or Makefile magic can help there.
 biesi also suggests an XUL preprocessor, which I don't know anything about.

(2) dump(func) is a bad idea.  That's something that slipped in from my original
code, sorry.  Ditto the dump right after setting mustBeTrue.

Comment 2

[Alex Vincent [:WeirdAl]]

There's no way mozilla.org will accept this.