foo in bar - 'in' operator javascript?

Question

I recently read a tutorial on CSS browser feature detection... The end product was something like this...

var prefix = [\'Moz\', \'webkit\', \'O\', \'ms\', \'Kht         


        

Answer 1

The in operator is used to check for the presence of a key in an array or object, e.g.

3 in [1, 2, 3] // false, since the array indices only go up to 2
2 in [1, 2, 3] // true
'x' in { x: 5 } // true
'toString' in Object.prototype // true

The style property there is an instance of CSSStyleDeclaration, which contains properties for each supported style attribute in the active browser.

The code snippet you gave in your post checks whether the viewing browser supports some version of that style (either the official one or with one of a number of common vendor prefixes).