Jasmine toBeUndefined

Question

I'm new to Jasmine and assumed using the .not.toBeDefined() or .toBeUndefined() matches you could check if a variable is undefined:

describe('toBeDefined', function() {

    it('should be defined', function() {
        var obj = {};
        expect(obj).toBeDefined(); // Passes
    });

    it('should not be defined using .not.tobeDefined()', function() {
        //var obj = {};
        expect(obj).not.toBeDefined(); // Fails // ReferenceError: obj is not defined
    });

    it('should not be defined using .tobeUnefined()', function() {
        //var obj = {};
        expect(obj).toBeUndefined(); // Fails // ReferenceError: obj is not defined
    });

});

I completely get that this would fail within the code, but I assumed using those matches, it wouldn't. Am I just using these wrong, or is it not possible to write a spec to check if something is undefined?

Solution 1

The problem is that

  expect(obj).toBeUndefined();

fails before the call to Jasmine even happens. It's erroneous to refer to a variable that's not defined (in new browsers or in "strict" mode at least).

Try this setup instead:

it('should not be defined using .tobeUnefined()', function() {
    var obj = {};
    expect(obj.not_defined).toBeUndefined(); 
});

In that code, there's a variable "obj" whose value is an empty object. It's OK in JavaScript to refer to a non-existent property of an object, and because such a reference results in undefined the test will pass. Another way to do it would be:

it('should not be defined using .tobeUnefined()', function() {
  var no_value;

  expect(no_value).toBeUndefined();
});

Solution 2

Note that your error says that obj is not defined.

It does not say that obj is undefined.

undefined is actually a data type in Javascript.

Any declared variable without an assignment is given a value of undefined by default, but that variable must be declared.

So when Jasmine tests whether a value is undefined, it is determining if obj === undefined.

If you declare

var obj;

then obj will test as undefined.

If you do not declare obj, then there is nothing for the Jasmine matcher to compare against the data type of undefined.