module.exports = onceonce.proto = once(function () {  Object.defineProperty(Function.prototype, ‘once‘, {    value: function () {      return once(this)    },    configurable: true  })})function once (fn) {  var f = function () {    if (f.called) return f.value    f.called = true    return f.value = http://www.mamicode.com/fn.apply(this, arguments)  }  f.called = false  return f}