Is there any way to use Jasmine default matchers within custom matchers?

Question

I have a custom matcher in some Jasmine test specs of the form:

this.addMatchers({
    checkContains: function(elem){
        var found = false;
        $.each( this.actual, function( actualItem ){

            // Check if these objects contain the same properties.
            found = found || actualItem.thing == elem;
        });
        return found;
    }
});

Of course, actualItem.thing == elem doesn't actually compare object contents- I have to use one of the more complex solutions in Object comparison in JavaScript.

I can't help but notice, though, that Jasmine already has a nice object equality checker: expect(x).toEqual(y). Is there any way to use that within a custom matcher? Is there any general way to use matchers within custom matchers?

Answer 1

Yes, it is slightly hacky but entirely possible.

The first thing we need to do is make the Jasmine.Env class available. Personally I have done this in my SpecRunner.html since its already setup there anyway. On the load of my SpecRunner I have the following script that runs:

(function() {
      var jasmineEnv = jasmine.getEnv();
      jasmineEnv.updateInterval = 1000;

      var trivialReporter = new jasmine.TrivialReporter();

      jasmineEnv.addReporter(trivialReporter);

      jasmineEnv.specFilter = function(spec) {
        return trivialReporter.specFilter(spec);
      };

      var currentWindowOnload = window.onload;

      window.onload = function() {
        if (currentWindowOnload) {
          currentWindowOnload();
        }
        execJasmine();
      };

      function execJasmine() {
        jasmineEnv.execute();
      };

    })();

So after the execJasmine function declaration I push the jasmineEnv into the global namespace by adding this:

this.jasmineEnv = jasmineEnv;

Now, in any of my spec files I can access the jasmineEnv variable and that is what contains the matchers core code.

Looking at toEqual specifically, toEqual calls the jasmine.Env.prototype.equals_ function. This means that in your customMatcher you can do the following:

beforeEach(function(){
    this.addMatchers({
        isJasmineAwesome    : function(expected){
            return jasmineEnv.equals_(this.actual, expected);
        }
    });
});

Unfortunately, using this method will only give you access to the following methods:

1. compareObjects_
2. equals_
3. contains_

The rest of the matchers reside the jasmine.Matchers class but I have not been able to make that public yet. I hope this helps you out in someway or another