Deserialize JSON into specific/existing JavaScript object

Question

Is there a way to parse a JSON string into an existing Javascript object: Lets say i have created this object:

var ClientState = function(){
    this.userId ="";
    this.telephoneState = "UNKNOWN";
    this.agentState = "UNKNOWN";
    this.muteState = "UNKNOWN";
    this.number = "";
    this.ready = false;
}

ClientState.prototype = {
    doNastyStuff: function(){
        //do something here
    }
    //other methods here
}

I have this json coming through the wire:

{"userId":"xyz","telephoneState":"READY","agentState":"UNKNOWN","muteState":"MUTED","number":"","ready":false}

Is it possible to deserialize into the object specified above? So that i can use all methods specified on it? Or in general is it possible to deserialize into a specific target object (without specifying deserialization in this target object)? (I know that i could create an constructor that accepts json or a parsed object.)

31piy · Accepted Answer · 2018-03-28 09:11:36Z

2

Yes! You can use Object.assign to overwrite the attributes of an object with another object:

var ClientState = function() {
  this.userId = "";
  this.telephoneState = "UNKNOWN";
  this.agentState = "UNKNOWN";
  this.muteState = "UNKNOWN";
  this.number = "";
  this.ready = false;
}

var c = new ClientState();
console.log('prior assignment: ', c);

Object.assign(c, {
  "userId": "xyz",
  "telephoneState": "READY",
  "agentState": "UNKNOWN",
  "muteState": "MUTED",
  "number": "",
  "ready": false
});

console.log('after assignment: ', c);

Note that it will overwrite all the properties of source object (first object) with the target object (second object) by matching the respective keys. The keys, which are non-existing in the target object are left intact in the source object.

answered Mar 28, 2018 at 9:11

31piy

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1 Comment

dermoritz Over a year ago

this is exactly what i need :-). Can i assign the json string directly or do i have to "parse" it first?

Máté Safranka · Accepted Answer · 2018-03-28 09:11:56Z

0

Is this what you had in mind?

function parseAs(targetClass, rawJSON) {
    return Object.assign(new targetClass(), JSON.parse(rawJSON));
}

var clientState = parseAs(ClientState, '{"userId":"xyz"}');

I don't think there's a native JSON method that does this, but you can just write a function like the one above. You can even define it on the JSON class itself:

JSON.parseAs = function(targetClass, rawJSON) {
    return Object.assign(new targetClass(), JSON.parse(rawJSON));
}

answered Mar 28, 2018 at 9:11

Máté Safranka

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Comments

Andy · Accepted Answer · 2018-03-28 09:17:09Z

0

If you want to use your function to add the object values to the instance properties:

function ClientState() {
  this.userId = "";
  this.telephoneState = "UNKNOWN";
  this.agentState = "UNKNOWN";
  this.muteState = "UNKNOWN";
  this.number = "";
  this.ready = false;
}

ClientState.prototype = {
  doNastyStuff: function(json) {
    const data = JSON.parse(json);
    Object.assign(this, data);
  }
}

const json = '{"userId":"xyz","telephoneState":"READY","agentState":"UNKNOWN","muteState":"MUTED","number":"","ready":false}';
const clientState = new ClientState();
clientState.doNastyStuff(json);
console.log(clientState);

answered Mar 28, 2018 at 9:17

Andy

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