systemjs/lib/polyfills.js

// Define an IE-friendly shim good-enough for purposes
var indexOf = Array.prototype.indexOf || function(item) { 
  for (var i = 0, thisLen = this.length; i < thisLen; i++) {
    if (this[i] === item)
      return i;
  }
  return -1;
}

var lastIndexOf = Array.prototype.lastIndexOf || function(c) {
  for (var i = this.length - 1; i >= 0; i--) {
    if (this[i] === c) {
      return i;
    }
  }
  return -i;
}