How to compare JavaScript objects in a unit test?

Question

I would like to know the proper way to compare objects in a unit test. For the purpose of this example, I am using assert and mocha to test a simple library mylib with a method method that returns an object.

var assert = require("assert");
var mylib = require("../src/mylib");

describe("method", function() {
  it("does something clever and returns an object", function() {
    assert.equal(
      JSON.stringify({/* expected object */}), 
      JSON.stringify(mylib.method(["items", "in", "the", "list"])));
  });
});

The above works, but I don't know if using JSON.stringify is a recommended practice. Am I doing this right?

t.niese · Accepted Answer · 2015-03-01 14:00:55Z

5

You should not use JSON.stringify, the problem with this approach is according to MDN JSON.stringify()

Properties of non-array objects are not guaranteed to be stringified in any particular order. Do not rely on ordering of properties within the same object within the stringification.

As of that you might compare {"a":2, "b":3} with {"b":3, "a":2}.

Instead of that you should use e.g. assert.deepEqual(to be honest I never used assert but as of the naming it should be the correct function)

answered Mar 1, 2015 at 14:00

t.niese

41k9 gold badges78 silver badges111 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Nick Tomlin Over a year ago

assert.deepEqual is spot on. Oh to think of the gymnastics I went through before I learned that it was there.

j-- Over a year ago

Thank you. Node's documentation was a bit lacking. Any particular reasons for not using assert?

t.niese Over a year ago

@JorgeBucaran no, I just like chai better, because the style is a bit more verbose e.g. expect(foo).to.deep.equal({ bar: 'baz' }); or expect(beverages).to.have.property('tea').with.length(3);. And in my opinion fits great into the way mocha is styled.

Or Assayag Over a year ago

expect(foo).to.deep.equal({ bar: 'baz' }); works for me

Collectives™ on Stack Overflow

How to compare JavaScript objects in a unit test?

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related