JavaScript Serializing and restoring class instances


Example

You can use a custom toJSON method and reviver function to transmit instances of your own class in JSON. If an object has a toJSON method, its result will be serialized instead of the object itself.

6
function Car(color, speed) {
  this.color = color;
  this.speed = speed;
}

Car.prototype.toJSON = function() {
  return {
    $type: 'com.example.Car',
    color: this.color,
    speed: this.speed
  };
};

Car.fromJSON = function(data) {
  return new Car(data.color, data.speed);
};
6
class Car {
  constructor(color, speed) {
    this.color = color;
    this.speed = speed;
    this.id_ = Math.random();
  }

  toJSON() {
    return {
      $type: 'com.example.Car',
      color: this.color,
      speed: this.speed
    };
  }

  static fromJSON(data) {
    return new Car(data.color, data.speed);
  }
}
var userJson = JSON.stringify({
  name: "John",
  car: new Car('red', 'fast')
});

This produces the a string with the following content:

{"name":"John","car":{"$type":"com.example.Car","color":"red","speed":"fast"}}
var userObject = JSON.parse(userJson, function reviver(key, value) {
  return (value && value.$type === 'com.example.Car') ? Car.fromJSON(value) : value;
});

This produces the following object:

{
  name: "John",
  car: Car {
    color: "red",
    speed: "fast",
    id_: 0.19349242527065402
  }
}