Convert between Map, Set, Object, Array, and JSON in JS

Map to Array

var map = new Map();
map.set(1, '111').set(2, '222').set(3, '333');
 
// map -> array
// 使用Array.from
var arr = Array.from(map); // [[1, "111"], [2, "222"], [3, "333"]]
 
// 使用...rest运算符 
var arr = [...map];  // [[1, "111"], [2, "222"], [3, "333"]]
// 或者 [...map.entries()]
 
// 使用for of循环 
var arr = [];
for (let [key, value] of map) {
	arr.push([key, value])
}
// 等同于上面 
// for (let [key, value] of map.entries()) {
//	    arr.push([key, value])
// }
 
 
// 使用forEach
var arr = [];
map.forEach(function(value, key, map) {
    arr.push([key, value])
});

Array to Map

// 一维数组 
var arr = ['one', 'two', 'three'];
 
var map = new Map(arr.map(function(value, key) {
    return [key, value]
}));     //  Map(3) {0 => "one", 1 => "two", 2 => "three"}
 
 
// 二维数组 
var arr = [[1, 'one'], [2, 'two'], [3, 'three']];
var map = new Map(arr);   //  Map(3) {1 => "one", 2 => "two", 3 => "three"}

Map to Object

var map = new Map();
map.set(1, '111').set(2, '222').set(3, '333');
 
// 使用for of
function mapToObj (map) {
    var obj = {};
    for (let [key, value] of map) {
        obj[key] = value;
    }
    return obj;
}
 
console.log(mapToObj (map));  // {1: "111", 2: "222", 3: "333"}

Convert Object to Map

var obj = {1: 'one', 2: 'two', 3: 'three'};
 
function ObjToMap (obj) {
    var map = new Map();
    for (let key in obj) {
        map.set(key, obj[key]);
    }
    return map;
}
 
console.log(ObjToMap (obj));  // Map(3) {"1" => "one", "2" => "two", "3" => "three"}

Convert Map to JSON String

var map = new Map();
map.set(1, '111').set(2, '222').set(3, '333');
 
// 使用for of
function mapToObj (map) {
    var obj = {};
    for (let [key, value] of map) {
        obj[key] = value;
    }
    return obj;
}
 
// 借助Map转成JSON字符串
function mapToJSONStr(map) {
    return JSON.stringify(mapToObj(map));
}
 
console.log(mapToJSONStr(map));  // '{"1":"111","2":"222","3":"333"}'

Convert JSON string to Map

var jsonStr = '{"1":"111","2":"222","3":"333"}';
 
function ObjToMap (obj) {
    var map = new Map();
    for (let key in obj) {
        map.set(key, obj[key]);
    }
    return map;
}
 
// 借助对象转成Map 
function JSONStrToMap(str) {
    return ObjToMap(JSON.parse(str));
}
 
console.log(JSONStrToMap(jsonStr));  // Map(3) {"1" => "111", "2" => "222", "3" => "333"}