手写代码

节流: 重复操作被忽略，直到完成

function throttle (callback, delay, immediate) {
  let context, args, timer;

  let run = () => {
    timer = setTimeout(() =>{
      !immediate && callback.apply(context, args);
      clearTimeout(timer);
      timer = null;
    }, delay)
  }

  return function() {
    context = this;
    args = arguments;

    if (timer) return
    !!immediate && callback.apply(context, args);
    run()
  }
}

防抖: 重复操作重置定时器

function debounce (callback, delay, immediate) {
  let timer, context, args;

  let run = () => {
    timer = setTimeout(() => {
      !immediate && callback.apply(context, args);
      clearTimeout(timer);
      timer = null;
    }, delay)
  }

  return function() {
    context = this;
    args = arguments;

    if (timer) {
      clearTimeout(timer);
      run()
    } else {
      !!immediate && callback.apply(context, args);
      run();
    }
  }
}

实现new

/**
 *  new 的过程
 * 1. 创建对象
 * 2. 设置原型链
 * 3. 绑定this
 * 4. 返回对象
 */
function _new () {
  const shift = Array.prototype.shift;
  const constructor = shift.call(arguments);
  
  if (typeof constructor !== 'function') throw new Error('第一个参数必须为函数')

  // 创建对象 + 设置原型链
  let obj = Object.create(constructor.prototype);
  // 绑定this
  let result = constructor.apply(obj, arguments);
  // 返回对象
  return result instanceof constructor ? result : obj;
}

function Car (name, price) {
  this.name = name
  this.price = price
}
const car1 = _new(Car, 'Benz', 10000)
const car2 = new Car ('Benz', 10000)

console.log(car1 instanceof Car, car2 instanceof Car)

实现call和apply

Function.prototype._call = function (target) {
  const fn = this;
  if (typeof fn !== 'function') throw new Error('调用者必须是函数')

  const type = typeof target;

  // 类型检测
  if (type === null || type === void 0) target = globalThis || new Function('return this')()

  if (!['object', 'function'].includes(type)) {
    const constructor = target.constructor;
    // 基本类型数据的处理:
    // 获得其构造函数，然后重新实例化成为一个对象类型
    // 使得其可以扩展属性
    target = new constructor(target)
  }
  // 推出队首内容，剩余的就是参数
  [...arguments].shift()
  target.fn = fn;
  // 执行函数
  let result = target.fn(...arguments)
  delete target.fn
  // 返回结果
  return result
}
Function.prototype._apply = function(target) {
  const fn = this;
  const type = typeof target;
  if (typeof fn !== 'function') throw new Error('调用者需要是函数')

  if (type === null || type === void 0) target = globalThis || new Function('return this')()
  if (!['object', 'function'].includes(type)) {
    const Constructor = target.constructor;
    target = new Constructor(target)
  }

  target.fn = fn;
  debugger
  const args = arguments[1];
  if (!Array.isArray(args)) {
    throw new Error('第二个参数请传递数组')
  }
  const result = target.fn(...args);

  delete target.fn;

  return result;
}

/**
 * 测试
 */
var obj = {
  name:'joy',
  getName(){
      console.log(this); //obj
      console.log(this.name); //joy
  }
};
var obj2 = {
  name: 'sam'
};
obj.getName._apply('sss', [1, 2, 3]) // {name: "sam", getName: ƒ}

// obj.getName() // {name: "joy", getName: ƒ}
obj.getName._call(obj2, 1, 2, 3) // {name: "sam", getName: ƒ}
obj.getName._call(1, 1, 2, 3) // {name: "sam", getName: ƒ}
obj.getName._apply(obj2, 1, 2, 3) // {name: "sam", getName: ƒ}

实现 Promise.all

/**
 * @description
 * Promise是ES6提供的一种解决异步机制的问题，替代了Generate
 * Promise有3种状态:
 * pending/fulfilled /rejected
 * 实例化时传入的callback内部是同步环境，异步内容会被处理.then 或者 .catch 中执行
 */

const _toString = Object.prototype.toString

/**
 * @param {*} promiseArr Promise数组
 */
Promise._all = function(promiseArr) {
  // 类型验证
  // ES6
  // if (!Array.isArray(promiseArr)) throw new Error('param type show be array')
  if (_toString.call(promiseArr) !== '[object Array]') 
    throw new Error('param type show be array')

  let results = [];
  let count = 0; // 记录被成功处理的promise
  let nocount = 0; // 记录被跳过的非promise数据
  return new Promise((resolve, reject) => {
    promiseArr.forEach((promise, index) => {
      // 简单类型验证
      if (_toString.call(promise) !== '[object Promise]') {
        nocount ++;
        return true; // 代替 continue
      }
      
      promise.then(res => {
        count++;
        results[index] = res;
        // 两个计数相加 = promiseArr长度，说明 promiseArr 被被处理完了
        if ((count + nocount) === promiseArr.length) {
          return resolve(results);
        }
      }, function(err) {
        return reject(err);
      });
    })
  });
};

// Testing
let p1 = new Promise((resolve, reject) => {
  setTimeout(_ => resolve(1), 0)
})

let p2 = new Promise((resolve, reject) => {
  setTimeout(_ => resolve(2), 1000)
})

let p3 = new Promise((resolve, reject) => {
  setTimeout(_ => resolve(3), 500)
})

let result = Promise._all([1,p1, p2, p3])
result.then(res => console.log(res))