indexOf.js

/**
 * Get position of given element in array or given sub-string in string
 * 
 * @raram  {String|Array}          source 
 * @param  {String|Number|Boolean} term
 * 
 * @return {Number}                       Position of term in source or -1
 */
var indexOf = (function () {
    var NEGATIVE = -1;
    var isArray = Array.isArray || function (source) {
        return Object.prototype.toString.call(source) === '[object Array]';
    };
    var isString = function (source) {
        return Object.prototype.toString.call(source) === '[object String]';
    };
    var handleArray = function (source, term) {
        for (var i = 0, len = source.length; i < len; i++) {
            if (source[i] === term) {
                return i;
            }
        }
        return NEGATIVE;
    };

    return function (source, term) {
        if (isArray(source)) {
            return source.indexOf ? source.indexOf(term) : handleArray(source, term);
        } else if (isString) {
            return source.indexOf(term);
        }
        return NEGATIVE;
    }
}());