Why use spyOn instead of jasmine.createSpy?

Question

What is the difference between

jasmine.createSpy(\'someMethod\')

And

spyOn(someObject, \'someMethod\')

Answer 1

Additionally to the other fine answer:

• Use spyOn() to spy (intercept) an existing method on an object to track calls of other modules to it.
• Use jasmine.createSpy() to create a function that can be passed as callback or Promise handler to track call-backs.

Answer 2

The difference is that you should have a method on the object with spyOn

const o = { some(): { console.log('spied') } };
spyOn(o, 'some');

while the mock method is created for your with createSpy():

const o = {};
o.some = jasmine.createSpy('some');

The advantage of the spyOn is that you can call the original method:

spyOn(o, 'some').and.callThrough();
o.some(); // logs 'spied'

And as @estus says the original method is restored after the test in case of spyOn. This should be done manually when it's reassigned with.