JSON.stringify not stringifying the whole object

Question

JSON.stringify(this.workout)is not stringifying the whole object. workoutis an object from the class Workout which looks like this:

export class Workout {
    id: string;
    name: string;
    exercises: Exercise[];
    routine: Routine;
}

Exercise and Routine is another Class with also nested arrays.

The problem is JSON.stringify(this.workout) return only {"name":"Day 1"}. Any ideas where the problem could be?

How this particular instance of Workout looks like? This one this.workout I guess if you are not setting all the properties with some values - JSON.stringify ignores undefined stuff. — ikos23
– ikos23, Commented Dec 4, 2018 at 21:47
Just like what John said, try checking what's inside your workout instance particularly your this.workout. It might be that only "name": "Day 1" is in there. — Paolo
– Paolo, Commented Dec 4, 2018 at 21:50
@john No, JSON.stringify() does not ignore null. It does ignore undefined. — Brad
– Brad, Commented Dec 4, 2018 at 21:51
@Brad I updated my comment because you are absolutely right. I've checked how it works ) — ikos23
– ikos23, Commented Dec 4, 2018 at 21:53

Brad · Accepted Answer · 2018-12-04 21:54:29Z

2

For any classes you wish to serialize, you may have to define your to toJSON() method to ensure the data is serialized. Otherwise, only the regular enumerable properties are going to end up in the output.

You'll probably need this on Exercise and Routine as well as Workout.

See also: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify

answered Dec 4, 2018 at 21:54

Brad

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Danziger · Accepted Answer · 2018-12-04 22:00:44Z

As you can see in this example with plain JS, it works as expected, so you should review your code and make sure all the objects are properly initialised.

Alternatively, you can also implement a custom toJSON method in any of those classes to define how you want to serialise them (check the example in class Routine):

class Exercises {
  constructor() {
    this.items = [1, 2, 3];
  }
}

class Routine {
  constructor() {
    this.property = 'DATA';
  }
  
  toJSON() {
    return `ROUTINE = ${ this.property }`;
  }
}

class Workout {
  constructor() {
    this.id = 1;
    this.name = 'Foo';
    this.exercises = new Exercises();
    this.routine = new Routine();
  }
}

const workout = new Workout();

console.log(JSON.stringify(workout, null, 4));

.as-console-wrapper {
  max-height: none !important;
}

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