Jasmine Matcher instanceof

jasmine.matcher.toBeInstanceOf.js

beforeEach(function() {
	this.addMatchers({
	    toBeInstanceOf: function(expectedInstance) {
	    	var actual = this.actual;
	    	var notText = this.isNot ? " not" : "";
	    	this.message = function() {
	    		return "Expected " + actual.constructor.name + notText + " is instance of " + expectedInstance.name;
	    	};
	    	return actual instanceof expectedInstance;
	    }		
	});
});

@grebett: Problem with that approach is the error message which is completely unhelpful. With jasmine.any you'll get a dump of what was actually passed in to the matcher:

Expected '12' to equal <jasmine.any(Number)>.

Instead of the much less helpful:

Expected false to be true.

I tough you could set up the output to the expectation as the second arg to .toEqual(), .toBeTruthy() and most expectation comparison does accept some kind of configuration argument.