Custom Equality Testers

You can customize how jasmine determines if two objects are equal by defining your own custom equality testers.

A custom equality tester is a function that takes two arguments. If the custom equality tester knows how to compare the two items, it should return either true or false. Otherwise, it should return undefined, to tell jasmine’s equality tester that it can’t compare the items.

function myCustomTester(first, second) {
  if (typeof first === 'string' && typeof second === 'string') {
    return first[0] === second[1];

Then, register your tester in a beforeEach so jasmine knows about it.

beforeEach(function() {

Now when you do comparisons in a spec, your custom equality testers will be checked first before falling back to the default equality tests. Note that if your custom tester returns false, no other equality checking will be performed.

it('is equal using a custom tester', function () {
  expect('abc').toEqual(' a ');

it('is not equal using a custom tester', function () {

it('works even in nested equality tests', function () {
  expect(['abc', '123'].toEqual([' a ', ' 1 ']);