Jasmine JavaScript Testing - toBe vs toEqual

javascript jasmine
Lloyd Banks picture Lloyd Banks · Mar 14, 2014 · Viewed 145.2k times · Source

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

elreimundo picture elreimundo · Jan 13, 2015

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.

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