Is it (`?:`) typescript ternary operator

Question

I saw the code below in a TypeScript example:

export interface EjectTaskOptions extends BuildOptions {
  force?: boolean;
  app?: string;
}

What does ?: mean? Is it a ternary operator (with only false condition) or something else?

https://www.typescriptlang.org/docs/handbook/interfaces.html — J. Steen, Apr 12 '17 at 11:07
the `?` is used for Optional Properties in an interface. http://www.typescriptlang.org/docs/handbook/interfaces.html — Claies, Apr 12 '17 at 11:09
https://www.xplatform.rocks/2016/01/07/angular2-quicky-elvis-in-tha-house/ — Yoav Schniederman, Apr 12 '17 at 11:40

score 24 · Accepted Answer · answered Apr 12 '17 at 11:11

24

The ? operator indicate that the property can be nullable / optional. It just means that the compilator will not throw an error if you do not implement this property in your implementation.

answered Apr 12 '17 at 11:11

LoïcR

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same as in `.NET` – mihail Apr 12 '17 at 11:31
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Except that .NET also has a null-coalescing ?? operator. @mihail – Jnr Jan 31 '19 at 07:45
Nullable/optional are *not* the same thing. Read more here: https://medium.com/@angela.amarapala/understanding-the-usage-of-optional-and-nullable-in-typescript-826c1754df3 – Arnab Datta Dec 16 '19 at 11:02

score 14 · Answer 2 · answered May 17 '20 at 01:41

14

You can use ?? operator!

const test: string = null;

console.log(test ?? 'none');

This will print 'none' because test is null. If there is a value for test, it will print that. You can try that here playground typescript

answered May 17 '20 at 01:41

Sasindu Lakshitha

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score 9 · Answer 3 · edited May 23 '17 at 12:18

9

Your code is nullable variable declaration

But the symbol of ?: using from Elvis operator

It Code looks like

let displayName = user.name ?: "";

And it's not available in typescript/javascript/angular and essentially the same as ||

More details : Comparison of Ternary operator, Elvis operator, safe Navigation Operator and logical OR operators

edited May 23 '17 at 12:18

Community

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answered May 18 '17 at 13:06

Ramesh Rajendran

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score 4 · Answer 4 · answered Apr 12 '17 at 11:34

4

The Elvis operator is only available for the . not for other dereference operators like [].

As a workaround use

{{ data?.record ? data.record['name/first'] : null}}

answered Apr 12 '17 at 11:34

Yoav Schniederman

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https://www.xplatform.rocks/2016/01/07/angular2-quicky-elvis-in-tha-house/ – Yoav Schniederman Apr 12 '17 at 11:40

Is it (`?:`) typescript ternary operator

4 Answers4