map 映射

函数定义

map<U>(callbackfn: (value: T, index: number, array: T[]) => U, thisArg?: any): U[];

一个简单的map映射示例

'use strict'

var list = [1, 2, 3, 4, 5];

var newList = list.map(value => value * 2);

console.log(newList);
// [ 2, 4, 6, 8, 10 ]

使用map映射对象数据，给每个元素添加新的属性

'use strict'

var list = [
    {
        name: "Tom",
        age: 10
    },
    {
        name: "Jack",
        age: 20
    }
];


var newList = list.map((item, index)=>{
    return {
        index: index,
        name: item.name,
        age: item.age + 1,
        active: false
    }
});


console.log(newList);
/**
[ 
    { 
        index: 0, 
        name: 'Tom', 
        age: 11, 
        active: false 
    },
    { 
        index: 1, 
        name: 'Jack', 
        age: 21, 
        active: false 
    } 
]
*/ 

forEach 迭代

函数定义

forEach(callbackfn: (value: T, index: number, array: T[]) => void, thisArg?: any): void;

使用 forEach 给列表添加属性

'use strict'

var list = [
    {
        name: "Tom",
        age: 10
    },
    {
        name: "Jack",
        age: 20
    }
];


list.forEach((item, index)=>{
        item.age = item.age + 1;
        item.active = false;
        item.index = index;
});


console.log(list);
/**
[ 
    { 
        name: 'Tom', 
        age: 11, 
        active: false, 
        index: 0 
    },
   { 
        name: 'Jack', 
        age: 21, 
        active: false, 
        index: 1 
    } 
]
*/ 

区别

map 和 forEach 都是迭代列表元素，参数都相同
map有返回值，forEach无返回值