Jasmine JavaScript Testing - toBe vs toEqual

Question

Let's say I have the following:

var myNumber = 5; expect(myNumber).toBe(5); expect(myNumber).toEqual(5); 

Both of the above tests will pass. Is there a difference between toBe() and toEqual() when it comes to evaluating numbers? If so, when I should use one and not the other?

Answer 1

For primitive types (e.g. numbers, booleans, strings, etc.), there is no difference between toBe and toEqual; either one will work for 5, true, or "the cake is a lie".

To understand the difference between toBe and toEqual, let's imagine three objects.

var a = { bar: 'baz' },     b = { foo: a },     c = { foo: a }; 

Using a strict comparison (===), some things are "the same":

> b.foo.bar === c.foo.bar true  > b.foo.bar === a.bar true  > c.foo === b.foo true 

But some things, even though they are "equal", are not "the same", since they represent objects that live in different locations in memory.

> b === c false 

Jasmine's toBe matcher is nothing more than a wrapper for a strict equality comparison

expect(c.foo).toBe(b.foo) 

is the same thing as

expect(c.foo === b.foo).toBe(true) 

Don't just take my word for it; see the source code for toBe.

But b and c represent functionally equivalent objects; they both look like

{ foo: { bar: 'baz' } } 

Wouldn't it be great if we could say that b and c are "equal" even if they don't represent the same object?

Enter toEqual, which checks "deep equality" (i.e. does a recursive search through the objects to determine whether the values for their keys are equivalent). Both of the following tests will pass:

expect(b).not.toBe(c); expect(b).toEqual(c); 

Hope that helps clarify some things.