Spying on jQuery $(‘…’) selector in jasmine

Spread the love

Question Description

When it comes to spying on jQuery functions (e.g. bind, click, etc) it is easy:

spyOn($.fn, "bind");

The problem is when you want to spy on $('...') and return defined array of elements.

Things tried after reading other related answers on SO:

spyOn($.fn, "init").andReturn(elements); // works, but breaks stuff that uses jQuery selectors in afterEach(), etc
spyOn($.fn, "merge").andReturn(elements); // merge function doesn't seem to exist in jQuery 1.9.1
spyOn($.fn, "val").andReturn(elements); // function never gets called

So how do I do this? Or if the only way is to spy on init function how do I “remove” spy from function when I’m done so afterEach() routing doesn’t break.

jQuery version is 1.9.1.

WORKAROUND:

The only way I could make it work so far (ugly):

realDollar = $;
try {
  $ = jasmine.createSpy("dollar").andReturn(elements);
  // test code and asserts go here
} finally {
  $ = realDollar;
}

Practice As Follows

Normally, a spy exists for the lifetime of the spec. However, there’s nothing special about destroying a spy. You just restore the original function reference and that’s that.

Here’s a handy little helper function (with a test case) that will clean up your workaround and make it more usable. Call the unspy method in your afterEach to restore the original reference.

function spyOn(obj, methodName) {
    var original = obj[methodName];
    var spy = jasmine.getEnv().spyOn(obj, methodName);
    spy.unspy = function () {
        if (original) {
            obj[methodName] = original;
            original = null;
        }
    };
    return spy;
}

describe("unspy", function () {
    it("removes the spy", function () {
        var mockDiv = document.createElement("div");
        var mockResult = $(mockDiv);

        spyOn(window, "$").and.returnValue(mockResult);
        expect($(document.body).get(0)).toBe(mockDiv);

        $.unspy();

        expect(jasmine.isSpy($)).toEqual(false);
        expect($(document.body).get(0)).toBe(document.body);
    });
});

As an alternative to the above (and for anyone else reading this), you could change the way you’re approaching the problem. Instead of spying on the $ function, try extracting the original call to $ to its own method and spying on that instead.

// Original
myObj.doStuff = function () {
    $("#someElement").css("color", "red");
};

// Becomes...
myObj.doStuff = function () {
    this.getElements().css("color", "red");
};

myObj.getElements = function () {
    return $("#someElement");
};

// Test case
it("does stuff", function () {
    spyOn(myObj, "getElements").and.returnValue($(/* mock elements */));
    // ...
});

You may be interested in these books.

Jasmine
$4.99
#ad

As an Amazon Associate I earn from qualifying purchases.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.