How to instantiate an object in TypeScript by specifying each property and its value?

Question

Here's a snippet in which I instantiate a new content object in my service:

const newContent = new Content(
     result.obj.name
     result.obj.user.firstName,
     result.obj._id,
     result.obj.user._id,
);

The problem is that this way of object instantiation relies on the order of properties in my content model. I was wondering if there's a way to do it by mapping every property to the value I want to set it to, for example:

 const newContent = new Content(
     name: result.obj.name,
     user: result.obj.user.
     content_id: result.obj._id,
     user_id: result.obj.user._id,
 );

Geoff Lentsch · Accepted Answer · 2017-07-28T02:21:54.890

23

const newContent = <Content>({
    name: result.obj.name,
    user: result.obj.user.
    content_id: result.obj._id,
    user_id: result.obj.user._id,
 });

Here you can instantiate an object and use type assertion or casting to the Content type. For more information on type assertion: https://www.typescriptlang.org/docs/handbook/basic-types.html#type-assertions

edited Jul 28 '17 at 02:21

answered Jul 27 '17 at 02:07

Geoff Lentsch

1,054
11
17

1

It is clear what you have changed, but it would be useful to say why. Teaching moments everywhere. – Anthony Horne Jul 27 '17 at 06:35
30

This is actually very very wrong! You're not instantiating an instance of `Content` here, you are creating a simple object which has the same members. If for example `Content` would have a method `fn`, then in your example this will fail: `newContent.fn()`. – Nitzan Tomer Sep 02 '18 at 14:07
2

this answer will work if you extend the prototype of the object like so: `const newContent = (_.extend({...}, Content.prototype));` – logeyg Oct 11 '18 at 20:11
As noted earlier, this would only work for an interface, which is what I'm using it for. – shturm Dec 02 '22 at 16:17

score 12 · Answer 2 · answered Apr 10 '17 at 04:07

You can pass an object to the constructor which wraps all of those variables:

type ContentData = {
    name: string;
    user: string;
    content_id: string;
    user_id: string;
}

class Content {
    constructor(data: ContentData) {
        ...
    }
}

And then:

const newContent = new Content({
     name: result.obj.name,
     user: result.obj.user.
     content_id: result.obj._id,
     user_id: result.obj.user._id,
});

How to instantiate an object in TypeScript by specifying each property and its value?

2 Answers2

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