js – find函数胡实现 (ES6语法)

1. Es6 中find用法

1. find() 方法返回数组中满足提供的测试函数的第一个元素的值 否则返回undefined

      var    number = [5, 12, 8, 130, 44];
      var    found = number.find(function (element) {
               return   element > 10;                                                  
      });
      console.log(found);    //结果12

2. 查找符合条件的指定元素

   var   inventory = [
         {name: 'apples',  quantity: 2},
         {name: 'bananas', quantity: 0},
         {name: 'cherries', quantity:5}
   ];
   name = inventory.find(function(element) {
          return   element.name === 'cherries';
   });
   console.info(name);  //得到结果 {name: 'cherries',  quantity: 5}   

3. 查找元素,返回找到的值,找不到返回undefined

   const   arr1 = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11];
   var   ret1 = arr1.find( (value, index, arr) => {
              return   value > 4
   } )
   var  ret2 = arr1.find( (value, index, arr) => {
              return    value > 14
   } )
   console.log('%s',  ret1)
   console.log('%s',  ret2)
   //执行结果   
   5
   undefined

2. findIndex 查找元素返回索引

1. 查找元素 返回找到的index, 找不到返回 -1

   var   ret3 = arr1.findIndex( (value, index, arr) => {
           return  value > 4
    } )
    var  ret4 = arr1.findIndex((value, index, arr) => {
             return  value > 14
    })
    console.log('%s', ret3)
    console.log('%s', ret4)
    结果:
    4
    -1

3. 实现方式

   var users = [
             {id: 1, name: '张三'},
             {id: 2, name: '张三'},
             {id: 3, name: '张三'},
             {id: 4, name: '张三'}
   ]
   Array.prototype.myFind = function(conditionFunc)  {
         //如果是返回索引则如下 
         // var conditionFunc = function (item, index) { return item.id === 4 }
         for (var i = 0; i < this.length; i++) {
               if (conditionFunc(this[i], i)) {
                   return this[i]
               }
        }
   }

  var ret = users.myFind(function (item, index) {
       return item.id === 2
   })

  console.log(ret)