在Javascript中将Map转换为JSON对象

Question

So Ive got the following javascript which contains a key/value pair to map a nested path to a directory.

function createPaths(aliases, propName, path) {
    aliases.set(propName, path);
}

map = new Map();

createPaths(map, 'paths.aliases.server.entry', 'src/test');
createPaths(map, 'paths.aliases.dist.entry', 'dist/test');

Now what I want to do is create a JSON object from the key in the map.

It has to be,

paths: {
  aliases: {
    server: {
      entry: 'src/test'
    },
    dist: {
      entry: 'dist/test'
    }
  }
}

Not sure if there is an out of a box way to do this. Any help is appreciated.

Answer 1

Given in MDN , fromEntries() is available since Node v12:

const map1 = new Map([
  ['foo', 'bar'],
  ['baz', 42]
]);

const obj = Object.fromEntries(map1);
// { foo: 'bar', baz: 42 }

For converting object back to map:

const map2 = new Map(Object.entries(obj));
// Map(2) { 'foo' => 'bar', 'baz' => 42 }

Answer 2

I hope this function is self-explanatory enough. This is what I used to do the job.

/*
 * Turn the map<String, Object> to an Object so it can be converted to JSON
 */
function mapToObj(inputMap) {
    let obj = {};

    inputMap.forEach(function(value, key){
        obj[key] = value
    });

    return obj;
}


JSON.stringify(returnedObject)

Answer 3

You could loop over the map and over the keys and assign the value

 function createPaths(aliases, propName, path) { aliases.set(propName, path); } var map = new Map(), object = {}; createPaths(map, 'paths.aliases.server.entry', 'src/test'); createPaths(map, 'paths.aliases.dist.entry', 'dist/test'); map.forEach((value, key) => { var keys = key.split('.'), last = keys.pop(); keys.reduce((r, a) => r[a] = r[a] || {}, object)[last] = value; }); console.log(object);

Answer 4

just using ES6 ways

1. Object.fromEntries

 const log = console.log; const map = new Map(); // undefined map.set(`a`, 1); // Map(1) {"a" => 1} map.set(`b`, 2); // Map(1) {"a" => 1, "b" => 2} map.set(`c`, 3); // Map(2) {"a" => 1, "b" => 2, "c" => 3} // Object.fromEntries ✅ const obj = Object.fromEntries(map); log(`\\nobj`, obj); // obj { a: 1, b: 2, c: 3 }

2. ...spread & destructuring assignment

 const log = console.log; const map = new Map(); // undefined map.set(`a`, 1); // Map(1) {"a" => 1} map.set(`b`, 2); // Map(1) {"a" => 1, "b" => 2} map.set(`c`, 3); // Map(2) {"a" => 1, "b" => 2, "c" => 3} const autoConvertMapToObject = (map) => { const obj = {}; for (const item of [...map]) { const [ key, value ] = item; obj[key] = value; } return obj; } const obj = autoConvertMapToObject(map) log(`\\nobj`, obj); // obj { a: 1, b: 2, c: 3 }

refs

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/fromEntries

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment

https://2ality.com/2015/08/es6-map-json.html

Answer 5

Another approach. I'd be curious which has better performance but jsPerf is down :(.

 var obj = {}; function createPaths(map, path, value) { if(typeof path === "string") path = path.split("."); if(path.length == 1) { map[path[0]] = value; return; } else { if(!(path[0] in map)) map[path[0]] = {}; return createPaths(map[path[0]], path.slice(1), value); } } createPaths(obj, 'paths.aliases.server.entry', 'src/test'); createPaths(obj, 'paths.aliases.dist.entry', 'dist/test'); console.log(obj);

Without recursion:

 var obj = {}; function createPaths(map, path, value) { var map = map; var path = path.split("."); for(var i = 0, numPath = path.length - 1; i < numPath; ++i) { if(!(path[i] in map)) map[path[i]] = {}; map = map[path[i]]; } map[path[i]] = value; } createPaths(obj, 'paths.aliases.server.entry', 'src/test'); createPaths(obj, 'paths.aliases.dist.entry', 'dist/test'); createPaths(obj, 'paths.aliases.dist.dingo', 'dist/test'); createPaths(obj, 'paths.bingo.dist.entry', 'dist/test'); console.log(obj);

 var obj = {}; function createPaths(map, path, value) { var map = map; var path = path.split("."); while(path.length > 1) { map = map[path[0]] = map[path.shift()] || {}; } map[path.shift()] = value; } createPaths(obj, 'paths.aliases.server.entry', 'src/test'); createPaths(obj, 'paths.aliases.dist.entry', 'dist/test'); createPaths(obj, 'paths.aliases.dist.dingo', 'dist/test'); createPaths(obj, 'paths.bingo.dist.entry', 'dist/test'); console.log(obj);