Create json string from js Map and String

Question

My REST controller expects request input of the following format, which it successfully converts to a Java object containing a Map and a String as parameters:

{ 
"myMap" : { 
    "key1": "value1", 
    "key2": "value2", 
    "key3": "value3"},
"myString": "string value"
}

I am getting my data from an html form like so:

var myMap = new Map();
var String = document.getElementById('String').value;
for (var i = 0 ; i<anArray.length ; i++){
    var input = document.getElementsByClassName('input_' + (i+1));
    for (var j = 0 ; j<3 ; j++){
        if (input[j].checked){
            myMap.set(input[j].name, input[j].id);
        }
    }
}

Basically, this code boils down to:

var myMap = new Map();
myMap.set("key1", "value1");
myMap.set("key2", "value2");
myMap.set("key3", "value3");

This results in a map containing {key1 => value1, key2 => value2, etc} and a String. I have been trying to turn this into a json string like so, but it doesn't seem to work:

var myJson = {};
myJson.myMap = myMap;
myJson.myString = myString;
var json = JSON.stringify(myJson);

However, I am ending up with the following string: `{"myMap":{},"String":"myString"}' . So I probably have to do something different to stringify a map, but nothing I try is working.

Can anyone help me out?

Answer 1

Using ES6 syntax, and especially if you have nested maps (otherwise Idan Dagan's answer is simpler), you can use the JSON.stringify()'s second argument, the reducer, as follows:

JSON.stringify(myMap, (key, value) => (value instanceof Map ? [...value] : value));

Answer 2

This hack will do the job (but it's a global override and must be used carefully):

  Map.prototype.toString = function() {

    let result = {};

    this.forEach((key, value) => { result[key] = value;});

    return JSON.stringify(result);
  };