手动封装一个forEacht和Map

手动封装一个数组方法：forEach

function myForEach(arr,callback){
	for(let i=0;i<arr.length;i++){
		callback(arr[i],i);
	}
}
myForEach([1,2,3],function(ele,index){
	console.log(ele,index)
})

挂载原型

      Array.prototype.myForEach = function(callback) {
        for (var i = 0; i < this.length; i++) {
          //封装的时候传入的第一个实参是值,第二个实参是索引
          callback(this[i], i);
        }
      };
      [1, 2, 3].myForEach((ele, index) => console.log(ele, index));

手动封装map

     function myMap(arr, callback) {
        let result = [];
        for (let i = 0; i < arr.length; i++) {
          result.push(callback(arr[i], i));
        }
        return result;
      }
      let res = myMap([1, 2, 3], function(ele, index) {
        // console.log(ele,index)
        return ele;
      });

挂载原型

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

       let res= [1,2,3].myMap((ele)=>ele*2)