原生方法

Array

1.forEach

  let arr = [
    { name: 'Eric', age: 18, sex: '男' },
    { name: 'Mary', age: 22, sex: '女' },
    { name: 'Rose', age: 25, sex: '女' },
  ]

  Array.prototype.xf_forEach = function (callback, curThis) { // 箭头函数不行？
    for (let i = 0; i < this.length; i++) {
      console.log('this是谁的',this);
      callback.bind(curThis, this[i], i, this)()
    }
  }

  arr.xf_forEach((item, index, curarr) => {
    console.log(item, index, curarr);
  })

2.map 返回一个新数组

  Array.prototype.xf_map = function (callback, curThis) {
    let res = [];
    for (let i = 0; i < this.length; i++) {
      res.push(callback.bind(curThis, this[i], i, this)());
    }
    return res;
  };

  arr.xf_map((item, index, curarr) => {
    console.log(item, index, curarr);
  })

3.filter

  Array.prototype.xf_filter = function (callback, curThis) {
    let res = []
    for (let i = 0; i < this.length; i++) {
      callback.call(curThis, this[i], i, this) && res.push(this[i])
    }
    return res
  }

  console.log(arr.xf_filter(item => item.age === 18)); // [ {name: 'Eric', age: 18, sex: '男'}]

4.every

  /**
   * callback(cur, index, this) cur 当前值、index当前下标、this遍历的对象
   * curThis 可选，若存在会被用作回调的this, 不存在 为 window 
   * 注意: curThis 在回调不为箭头函数时才能有正确指向
   * 23-4.4修改
   */

  Array.prototype.xf_every = function (callback, curThis) {
    let flag = true;
    let len = this.length;

    for (let i = 0; i < len; i++) {
      flag = callback.call(curThis, this[i], i, this); // 改变函数执行时的指向
      if (!flag) break;
    }
    return flag;
  };

  console.log(arr.xf_every(item => item.age >= 22)); // false

5.some

  Array.prototype.xf_some = function (callback, curThis) {
    let flag = false;
    for (var i = 0; i < this.length; i++) {
      flag = callback.apply(curThis, [this[i], i, this]);
      if (flag) break;
    }

    return flag;
  };

  console.log(arr.xf_some(item => item.age > 25)); // false

6.findIndex

  Array.prototype.xf_findIndex = function(callback, curThis) {
    // if()
    for(let i = 0; i < this.length; i++){
      if(callback.apply(curThis, [this[i], i ,this])){
        return i
      }
    }
    return -1
  }

  console.log(arr.xf_findIndex(item => item.age === 18)); // 0

7.find

  Array.prototype.xf_find = function(callback, curThis) {
    for(let i = 0; i < this.length; i++){
      if(callback.call(curThis, this[i], i ,this)){
        return this[i]
      }
    }
    return undefined
  }

  console.log(arr.xf_find(item => item.age === 18)); // {name: 'Eric', age: 18, sex: '男'}

8.join

let arr1 = [1, 2, 3]

Array.prototype.xf_join = function(s) {
    let str = ''
    for(let i = 0; i < this.length; i++){
      str = i === 0 ? `${str}${this[i]}`: `${str}${s}${this[i]}`
    }
    return str
  }

  console.log(arr1.xf_join('+')); // 1+2+3

9.flat

let arr3 = [1, [2, 3, [4, 5]], [8, 9]]

Array.prototype.xf_flat = function() {
    let arr = this
    while(arr.some(item => Array.isArray(item))){
      arr = [].concat(...arr)
    }
    return arr
  }
  console.log(arr3.xf_flat()); //  [1, 2, 3, 4, 5, 8, 9]