Parse JSON to TypeScript object

Question

Let say I have a Object:

class Person{
id: number;
name: string;
}

And Json from API:

{
"id": "10",
"name": "Person Name",
"email": "[email protected]"
}

How to convert from JSON to Person object, excatly variables that is in Person class?

I tried this:

Object.assign(Person.prototype, this.jsonList))

but i'ts not working

Add a constructor, and call it: new Person(json.id, json.name)? — JB Nizet
– JB Nizet, Commented May 27, 2017 at 14:34
Method Object.assign assigns all properties, but email doesnt exists in Person — Emis
– Emis, Commented May 27, 2017 at 14:35

score 1 · Accepted Answer · 2017-05-27 15:01:53Z

1

The information about what properties are declared in a class is "metadata", and is not directly accessible. Hence, there is no straightforward way to copy only those properties present in a class from some input which might contain additional unwanted properties, other than explicitly enumerating them.

The feature of JavaScript/TypeScript which does have access to such metadata is decorators. Therefore, to solve your problem in a generalized way requires such a decorator. The decorator could generate a static method which copied just those properties which actually exist on the class. That would look like that:

@ConstructFromJsonWithExtraGarbage()
class Person {
}

const sally = Person.constructWithExtraGarbage(
  {id: 1, name: "Sally", email: "[email protected]"});

Actually writing this decorator is beyond the scope of this answer.

edited May 27, 2017 at 15:01

answered May 27, 2017 at 14:35

user663031

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7 Comments

Emis Over a year ago

I don't need email. Object.assign method copies all properties

Emis Over a year ago

there can be a lot of unnecessary properties in Json. I need exactly which are described in Person. I need mapping approach. But Object.assign extends Person with all properties

JB Nizet Over a year ago

So replace Object.assign() by this.id = person.id; this.name = person.name;. What's the concrete problem?

Emis Over a year ago

This is the problem, I must write all properties by hand, I cant find auto mapper.

user663031 Over a year ago

What you want is a "class decorator". You can find more information at typescriptlang.org/docs/handbook/decorators.html.

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