ES6中的Map与JSON的相互转化（序列和持久化）

1. 将Map对象转化成为二维数组

1.1. 将Map和数组对相互转化

> let myMap = new Map().set(true, 7).set({foo: 3}, ['abc']);
> [...myMap]
[[true, 7], [Object { foo=3}, ["abc"]]]

> new Map([[true, 7], [{foo: 3}, ['abc']]])
Map {true => 7, Object {foo: 3} => ['abc']}

1.2 与JSON的相互转化

function mapToJson(map) {
    return JSON.stringify([...map]);
}

function jsonToMap(jsonStr) {
    return new Map(JSON.parse(jsonStr));
}

> let myMap = new Map().set(true, 7).set({foo: 3}, ['abc']);
> mapToJson(myMap)
'[[true,7],[{"foo":3},["abc"]]]'
> jsonToMap('[[true,7],[{"foo":3},["abc"]]]')
Map {true => 7, Object {foo: 3} => ['abc']}

2. 通过objects将Map序列化为JSON

2.1 将Map和object进行相互转化

function strMapToObj(strMap) {
    let obj = Object.create(null);
    for (let [k,v] of strMap) {
        // We don’t escape the key '__proto__'
        // which can cause problems on older engines
        obj[k] = v;
    }
    return obj;
}

function objToStrMap(obj) {
    let strMap = new Map();
    for (let k of Object.keys(obj)) {
        strMap.set(k, obj[k]);
    }
    return strMap;
}

> let myMap = new Map().set('yes', true).set('no', false);
> strMapToObj(myMap)
{ yes: true, no: false }
> objToStrMap({yes: true, no: false})
[ [ 'yes', true ], [ 'no', false ] ]

function strMapToJson(strMap) {
    return JSON.stringify(strMapToObj(strMap));
}

function jsonToStrMap(jsonStr) {
    return objToStrMap(JSON.parse(jsonStr));
}

> let myMap = new Map().set('yes', true).set('no', false);
> strMapToJson(myMap)
'{"yes":true,"no":false}'
> jsonToStrMap('{"yes":true,"no":false}');
Map {'yes' => true, 'no' => false}