raptor-polyfill/array/lastIndexOf.js

Polyfills for various EcmaScript 5 and EcmaScript 6 methods distributed as CommonJS modules that can be require'd individually or as a whole.

// ES5 15.4.4.15
// http://es5.github.com/#x15.4.4.15
// https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/lastIndexOf
if (!Array.prototype.lastIndexOf) {
    var toObject = require('./_toObject');
    var toInteger = require('./_toInteger');

    Array.prototype.lastIndexOf = function lastIndexOf(sought /*, fromIndex */) {
        var self = toObject(this),
            length = self.length >>> 0;

        if (!length) {
            return -1;
        }
        var i = length - 1;
        if (arguments.length > 1) {
            i = Math.min(i, toInteger(arguments[1]));
        }
        // handle negative indices
        i = i >= 0 ? i : length - Math.abs(i);
        for (; i >= 0; i--) {
            if (i in self && sought === self[i]) {
                return i;
            }
        }
        return -1;
    };
}