Whats the easiest way to create a TypeScript object with JSON as input?

Question

In Angular2 (TypeScript) I have a class with the following constructor:

 export class DataModel {
    constructor(public date_of_visit: string,
                public gender: boolean,
                public year_of_birth: number,
                public height: number,
                public weight: number){}
 }

I have the following JSON object:

json = {"date_of_visit": "23/09/2016", "gender": 1, "year_of_birth": 1975, "height":185, "weight": 85}

Question: Whats the easiest way to create a DataModel instance with the JSON data as input? Something like new DataModel(**json)

Possible duplicate of JSON to TypeScript class instance?

madreason
– madreason

2016-10-12 11:42:03 +00:00
Commented Oct 12, 2016 at 11:42 — madreason
– madreason, Commented Oct 12, 2016 at 11:42

Marin Relatic · Accepted Answer · 2016-10-11 11:20:09Z

1

For compile time casting, this will do:

let dataModel = {"date_of_visit": "23/09/2016", "gender": 1, "year_of_birth": 1975, "height":185, "weight": 85} as DataModel;

answered Oct 11, 2016 at 11:20

Marin Relatic

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5 Comments

John Weisz Over a year ago

FYI, this is a type-assertion, which is a compile-time construct, and not a type-cast, which would be a runtime-time construct. This effectively means that the object created from parsing the JSON will be an Object instance at runtime, and not a DataModel instance. This is fine as long as you don't use instanceof, or define methods, getters, setters, or anything that is not inherently present in the parsed JSON itself.

Vingtoft Over a year ago

Thanks for clarifying that @JohnWhite. I think the answer Im looking for is type-cast, because I need to call methods of DataModel. Can you show an example of this?

Vingtoft Over a year ago

I think I found the answer here: stackoverflow.com/questions/32167593/…

John Weisz Over a year ago

IMO, this is a complete unknown in TypeScript for now. There is no standardized methodology for doing an actual type-cast, which can be credited to the relatively young age of TypeScript, and that one of its goals is minimizing any runtime overhead. However, there's an experimental project I started working on, TypedJSON, which does exactly what you are looking for: creating a user-defined class instance from JSON. It has its limitations, but it is solid for general use, and its syntax is extremely lightweight. I can post an answer with it.

Vingtoft Over a year ago

I'll take a look at your project, thanks for your guidance.

Pradeep · Accepted Answer · 2016-10-11 11:25:26Z

0

Casting should get you through:

let model: DataModel = {"date_of_visit": "23/09/2016", "gender": 1, "year_of_birth": 1975, "height":185, "weight": 85} as DataModel;

edited Oct 11, 2016 at 11:25

answered Oct 11, 2016 at 11:18

Pradeep

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1 Comment

John Weisz Over a year ago

It is worth noting that the preferred way of doing a type-assertion is obj as Type.

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