手写 call、applay、bind

 

call

Function.prototype.mycall = function(context, ...args) {
  if (this === Function.prototype) {
    return undefined;
  }
  context = context || window;
  const fn = Symbol();
  context[fn] = this; // this就是 调用的函数
  const result = context[fn](...args); // 
  delete context[fn];
  return result;
}

实现逻辑如下，把函数给这个对象，然后通过对象的方式调用，this 就指向这个 对象了

function test(...args) {
  console.log(this.name, ...args);
}
let obj = {
  name: 'lisi'
}
obj.fn = test;
obj.fn(1,2);

apply 只是参数处理不一样

Function.prototype.myapply = function(context, args = []) {
  if (this === Function.prototype) {
    return undefined;
  }
  context = context || window;
  const fn = Symbol();
  context[fn] = this; // this就是 调用的函数
  const result = context[fn](...args); // 
  delete context[fn];
  return result;
}

 bind

Function.prototype.mybind = function(context, ...args) {
  if (this === Function.prototype) {
    return undefined;
  }
  if (!context) {
    return this;
  }
  const fun = this;
  return  function(...args1) {
    return fun.call(context, ...[...args,...args1]);
    // 或者如下
    // const fn = Symbol();
    // context[fn] = fun;
    // const result = context[fn](...[...args,...args1]);
    // delete context[fn];
    // return result;
  };
}