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    <title>Document</title>
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<body>
     <script>
         let arr1 = [1,2,3,4,5,6,7,8,9];
         //push 数组末尾添加元素
         arr1.push(10);
         console.log(arr1);
         //pop  数组末尾删除元素
         arr1.pop();
         console.log(arr1);
        //shift 数组开头删除元素
        arr1.shift();
        console.log(arr1);
        //unshift  数组开头添加元素
        arr1.unshift(1);
        console.log(arr1);
        //splice  修改、添加、删除元素均可
        
        
         //map 为每个元素执行函数语句并将原数组元素替换为执行结果
         let arr2 = arr1.map(item=>item*2);
         // [2,4,6,8,10,12,14,16,18]
         console.log(arr2)

         //filter  为每个元素执行函数语句并将符合条件的数组返回
         let arr3 = arr1.filter(item =>item%2==0);
         //[2,4,6,8]
         console.log(arr3)

         //reduce  Replace .filter().map() with .reduce()
         //https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce
         
         //eg1:数组元素累计求和
         let sum = arr1.reduce((accumulator,currentValue)=>accumulator+currentValue);
         console.log(sum); //45

        //eg2: 累加对象数组里的值   要累加对象数组中包含的值，必须提供初始值，以便各个item正确通过你的函数。
        var initialValue = 0;
        var sum2 = [{x: 1}, {x:2}, {x:3}].reduce(function (accumulator, currentValue) {
            return accumulator + currentValue.x;
        },initialValue)
        console.log(sum2) // logs 6

        //eg3: 数组去重   es6写法 Array.from(new Set(arr))   或者  [...new Set(arr)]
        let myArray = ['a', 'b', 'a', 'b', 'c', 'e', 'e', 'c', 'd', 'd', 'd', 'd']
        let myOrderedArray = myArray.reduce(function (accumulator, currentValue) {
        if (accumulator.indexOf(currentValue) === -1) {
            accumulator.push(currentValue)
        }
        return accumulator
        }, [])

        console.log(myOrderedArray)

        //eg4: 按属性对object分类
        var people = [
            { name: 'Alice', age: 21 },
            { name: 'Max', age: 20 },
            { name: 'Jane', age: 20 }
        ];

        function groupBy(objectArray, property) {
            return objectArray.reduce(function (acc, obj) {
                var key = obj[property];
                if (!acc[key]) {
                acc[key] = [];
                }
                acc[key].push(obj);
                return acc;
            }, {});
            }

        var groupedPeople = groupBy(people, 'age');
        console.log(groupedPeople)
     </script>
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posted on 2021-04-30 14:13 巍MG 阅读(59) 评论(0) 收藏举报
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