Array.indexOf
Summary
Return the first index at which a given element can be found in the array, or -1 if it is not present.(It's just created on old browsers which haven't got this method natively)
Syntax
Array.indexOf(value)
Example
>>> var list = [3,5,7,9]
>>> list.indexOf(3)
0
Examples
Example #1: Create an array and find an item's index.
Source files of the above example:
../../examples/indexOf.js
var fruits = ['Apple','Cherry','Grape','Banana'];
document.write(fruits.indexOf("Grape"));