实现apply.js

Function.prototype.myapply = function(context) {
  if (typeof this !== "function") {
    throw new TypeError("not function");
  }
  // 如果传递的执行上下文为null，就将环境切换为window
  context = context || window;
  // 然后在context对象上新建一个属性,是一个函数
  context.fn = this;
  //    这个地方是取参数
  let result;
  if (arguments[1]) {
    result = context.fn(...arguments[1]);
  } else {
    result = context.fn();
  }
  //  删除了这个属性
  delete context.fn;
  return result;
};

Function.prototype.Myapply = function(context = window, args) {
  if (typeof this !== "function") {
    throw new TypeError("不是函数");
  }
  context = context || window;
  context.fn = this;
  if (Array.isArray(args)) {
    result = context.fn(...args);
  } else {
    result = context.fn();
  }
  delete context.fn;
  return result;
};

Function.prototype.MyApply = function(context, arg) {
  if (typeof this !== "function") {
    throw new TypeError(`not function`);
  }
  let fn = new Symbol();
  context[fn] = this;
  let result;
  if (Array.isArray(arg)) {
    result = context[fn](...arg);
  } else {
    result = context[fn]();
  }
  delete context.fn;
  return result;
};