Make Assertion.prototype properties configurable

[jfirebaugh]

This allows plugins to install object-specific behavior for built-in
assertions.

I'm working on an assertion library for jQuery (inspired by https://github.com/velesin/jasmine-jquery).
The goal is to write assertions like:

$('#foo').should.exist;
$('#foo').should.contain('#bar');

These would be implemented by overriding the existing properties, e.g.:

chai.use(function (chai) {
  var chaiExist = Object.getOwnPropertyDescriptor(chai.Assertion.prototype, 'exist');
  Object.defineProperty(chai.Assertion.prototype, 'exist', {
    get : function () {
      if (this.obj instanceof jQuery) {
        this.assert(
            this.obj.length > 0
          , 'expected ' + inspect(this.obj.selector) + ' to exist'
          , 'expected ' + inspect(this.obj.selector) + ' not to exist');
        return this;
      } else {
        return chaiExist.get.call(this);
      }
    }
  });
});

But in order for this to work, the original Object.defineProperty needs to have
been passed configurable: true.

I'm also amenable to other suggestions as to how to accomplish this.

[logicalparadox]

I am quite fine with this... and excited to see what you come up with!

[logicalparadox]

In release 0.3.3.

Please keep me apprised of your progress :)

[jfirebaugh]

Thanks!

Here's the library: https://github.com/jfirebaugh/chai-jquery

[logicalparadox]

This is awesome!! Great stuff!!

I will set up a plugin section in the readme and docs today.