performance difference between location.href and window.location.href

Question

I have been read location.href is faster than window.location.href. But internally location.href is being read as window.location.href right? So how it would increase the significant performance?

Answer 1

I have been read location.href is faster than window.location.href.

It might be infinitessimally faster, but nothing you'd notice in real life. Here's why:

Here's what the engine does (in theory) when it sees location.href:

• Looks up location in the current scope; if not found, goes to the containing scope and so on, eventually reaching global scope.
• At global scope, location is found as a property of the global object.
• Then it looks up the href property on the location object.

Here's what the engine does (in theory) when it sees window.location.href:

• Looks up window in the current scope; if not found, goes to the containing scope and so on, eventually reaching global scope.
• At global scope, window is found as a property of the global object; it's a property the global object uses to refer to itself.
• Then it looks up the location property on that object.
• Then it looks up the href property on the location object.

So window.location.href requires one more property lookup than location.href does — barring any optimizations the JavaScript engine might be able to apply. But JavaScript performance is incredibly variable from engine to engine; your mileage may vary. Here's a benchmark that FB55 put together showing that the theory above is borne out by experimental results; location.href is indeed faster. In that particular test.

(Blue = location.href, red = window.location.href; longer lines = faster performance.)

More to the point: Does it really matter? Not in the real world, no. You'd have to be doing this millions of times for there to be any human-perceptible difference. But that's the explanation for why you'll see people saying this about globals like location (or any other global, built-in or added by your own code).