How to initialize and return an object in a single line

Question

I am trying to create Option objects based on the following typed interface:

interface Option {
    /** Text for rendering */
    label: string;
    /** Value for searching */
    value: string | number;
    /**
     * Allow this option to be cleared
     * @default true
     */
    clearableValue?: boolean;
}

Is it possible to convert the following to a single line?

const options = [1, 2, 3].map<Option>((t) => {
    const option: Option = { label: String(t), value: String(t) };
    return option;
});

I tried:

const options = [1, 2, 3].map<Option>((t) => Option = { label: String(t), value: String(t) });

but it doesn't work.

Aleksey L. · Accepted Answer · 2016-11-02T16:18:58.653

1

You're almost there:

const options = [1, 2, 3].map(t => <Option>{ label: String(t), value: String(t) });

Type assertion <Option>{ label: String(t), value: String(t) } can also be done with as operator: t => ({ label: String(t), value: String(t) }) as Option

Update: As you've already figured out - the first option (<Option>) creates ambiguity in *.tsx files, so as syntax is preferred.

edited Nov 02 '16 at 16:18

answered Nov 02 '16 at 06:53

Aleksey L.

35,047
10
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The first suggestion has an error: "Symbol 'label' cannot be properly resolved, probably it is located in inaccessible module". Is it normal? I am using TypeScript 1.8. The second suggestion works fine. – Erwin Mayer Nov 02 '16 at 07:42
Try to put object initializer into brackets ` – Aleksey L. Nov 02 '16 at 08:01
No it doesn't help. Maybe this wasn't supported before TS2. Unless there is a way to make it work, you could update your reply to differentiate between the two versions and I'll mark it as accepted. – Erwin Mayer Nov 02 '16 at 08:04
Indeed, it seems due to the fact that I am in a *.tsx file and – Erwin Mayer Nov 02 '16 at 15:09
https://basarat.gitbooks.io/typescript/content/docs/tips/genericTSX.html – Erwin Mayer Nov 02 '16 at 15:11
A bit hackish, there doesn't seem to be a good solution. If you can update your answer to reflect that it'll probably save some time to people. – Erwin Mayer Nov 02 '16 at 15:13

score 0 · Answer 2 · answered Nov 02 '16 at 06:53

0

You could use a typescript cast:

const options = [1, 2, 3].map<Option>((t) => <Option>{ label: String(t), value: String(t) } );

answered Nov 02 '16 at 06:53

CortoMaltese

131
6

This triggers an error: "Symbol 'label' cannot be properly resolved, probably it is located in inaccessible module". Is it normal? I am using TypeScript 1.8. – Erwin Mayer Nov 02 '16 at 07:42
I tried it in the typescript playground without any errors. I am sorry that this obviously does not work in your environment. – CortoMaltese Nov 02 '16 at 08:05

How to initialize and return an object in a single line

2 Answers2