Explanation for: "function" == typeof code?

Question

I am working on someone script and I don't understand following line. Can someone explain me this line?

 var self = this,
 "function" == typeof self.options.callback && self.options.callback.call(self)
 callback: function() { .. }

options is object

Look like a conditional statement but used as an expression! — Afzaal Ahmad Zeeshan, Jul 15 '14 at 18:24
Thankx for quick replay, but how that function call when i remove this line from script I am getting error. There is callback function but I am not sure how that function call here? Can you explain me this? — Marmik Desai, Jul 15 '14 at 18:26
For the odd code, see the marked duplicate. If you don't understand what the `("function" == typeof self.options.callback)` part means, check the [MDN docs on the `typeof` operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/typeof) — Bergi, Jul 15 '14 at 18:30
when I console "self.options.callback" this line i am getting callback function, but when i console "self.options.callback.call(self)" this line i am getting undefined. Addition if I remove "self.options.callback.call(self)" this my script doesn't work... — Marmik Desai, Jul 15 '14 at 18:32
@simpleclick: Uh, [`.call(self)`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call) just calls that function and returns the result? What else is it that you are asking about? — Bergi, Jul 15 '14 at 20:11

Benjamin Trent · Answer 1 · 2014-07-15T18:30:43.617

1

It is verifying that the type of self.options.callback is a function and that self.options.callback.call(self) is resolved to true.

The typeof operator returns a string indicating the type of the unevaluated operand.

edited Jul 15 '14 at 18:30

answered Jul 15 '14 at 18:25

Benjamin Trent

`typeof` can't span the `&&` – charlietfl Jul 15 '14 at 18:29
yes, I realize after reading the inquiry code more closely. – Benjamin Trent Jul 15 '14 at 18:29
cool, just noticed update – charlietfl Jul 15 '14 at 18:30
so it will check "self.options.callback" is function, if it is function than it will return true? is that what you mean? – Marmik Desai Jul 15 '14 at 18:38
@simpleclick exactly, and of course the conditional statement continues to check if `self.options.callback.call(self)` returns true. – Benjamin Trent Jul 15 '14 at 18:39

1 Answers1