IE shims for array indexOf, string startsWith and string trim

ie-shims.js

// Some common IE shims... indexOf, startsWith, trim

/*
  Really? IE8 Doesn't have .indexOf
*/
if (!Array.prototype.indexOf) {
  Array.prototype.indexOf = function (searchElement /*, fromIndex */ ) {
    "use strict";
    if (this === null) {
      throw new TypeError();
    }
    var t = Object(this);
    var len = t.length >>> 0;

    if (len === 0) {
      return -1;
    }
    var n = 0;
    if (arguments.length > 1) {
      n = Number(arguments[1]);
      if (n != n) { // shortcut for verifying if it's NaN
        n = 0;
      } else if (n !== 0 && n != Infinity && n != -Infinity) {
        n = (n > 0 || -1) * Math.floor(Math.abs(n));
      }
    }
    if (n >= len) {
      return -1;
    }
    var k = n >= 0 ? n : Math.max(len - Math.abs(n), 0);
    for (; k < len; k++) {
      if (k in t && t[k] === searchElement) {
        return k;
      }
    }
    return -1;
  };
}

/*
  IE Doesn't have a .startsWith either?
*/
if (!String.prototype.startsWith) {
  String.prototype.startsWith = function (str){
    return this.lastIndexOf(str, 0) === 0;
  };
}

// IE < 9 doesn't have a trim() for strings
if (!String.prototype.trim) {
  String.prototype.trim = function () {
    return this.replace(/^\s+|\s+$/g, '');
  };
}