手写call-apply-bind

1. call

/**
 * rewrite call
 * https://tc39.es/ecma262/#sec-function.prototype.call
 */

Function.prototype._call = function (ctx) {
  ctx = Object(ctx) || window
  ctx.fn = this

  var args = []
  for (var i = 1; i < arguments.length; i++)
    args.push('arguments[' + i + ']')
  var result = eval('ctx.fn(' + args + ')')

  delete ctx.fn
  return result
}

2. apply

/**
 * rewrite apply
 * https://tc39.es/ecma262/#sec-function.prototype.apply
 */

Function.prototype._apply = function (ctx, args) {
  ctx = Object(ctx) || window
  ctx.fn = this
  var _toString = Object.prototype.toString
  var result
  
  // args is primitive value
  if (args && typeof args !== 'object') {
    throw new TypeError("CreateListFromArrayLike called on non-object")
  }

  if (!args || _toString.call(args).slice(8, -1) !== 'Array') {
    result = ctx.fn()
  } else {
    result = eval('ctx.fn(' + args + ')')
  }

  delete ctx.fn
  return result
}

3. bind

/**
 * rewrite bind
 * https://tc39.es/ecma262/#sec-function.prototype.bind
 */

Function.prototype._bind = function (ctx) {
  var originFn = this,
      args = [].slice.call(arguments, 1)
  
  // 原型传递中介函数
  // var _tempFn = function () { }

  var newFn = function () {
    var newArgs = [].slice.call(arguments)
    // new newFn(), this -> 实例对象,
    // newFn(), this -> ctx
    return originFn.apply(this instanceof newFn ? this : ctx, args.concat(newArgs))
  }

  // 第一种方式
  // 与原生bind行为保持一致, newFn原型指向originFn原型
  newFn.prototype = originFn.prototype

  // 第二种方式
  // 与原生bind行为不一致, 利用中介函数_tempFn充当originFn原型
  // _tempFn.prototype = originFn.prototype
  // newFn.prototype = new _tempFn()

  return newFn
}