Proposed question: 5 ways to call a JavaScript function?

[whawker]

This is a question I was once asked in a job interview. Might be appropriate here.

http://devlicio.us/blogs/sergio_pereira/archive/2009/02/09/javascript-5-ways-to-call-a-function.aspx

[dpashkevich]

+1, only I would rather call it "5 ways to set function execution context"

[davemackintosh]

I second dpashkevich on this. Good question though!

[nathansmith]

Good suggestion, I don't disagree that it's good knowledge to have.

But, I feel like aspects of that blog post are already covered…

• apply()
• call()
• using constructors
• global scope

[dpashkevich]

Right, but it's a less direct question. You can see how the person understands that all above is connected.

[nathansmith]

I'm up for adding it. Care to write a question, and an example answer?

[dpashkevich]

I kept going back and forth with the question phrasing, here's the best I've come up so far:

Question
Can you think of 5 different ways a this can be set when calling a function?

Answer

• 1. Global function call

foo();  // this === global inside the function

• 2. Method call

obj.foo();  // this === obj inside the function

• 3,4. Function.call() and Function.apply()

foo.call(obj, param1, param2, param2);  // this === obj
foo.apply(obj, [param1, param2, param2]);  // this === obj

• 5. Constructor call

new Foo();  // this === empty object with Foo's prototype

[mpatel3]

+1