Is there an Angular @input attribute that concludes with an exclamation mark?

This source code showcases the usage of @Input properties with an exclamation mark (!) at the end. An example is shown below:

@Input() token!: StripeToken

The presence of ! in this case signifies a non-null assertion operator, but what is the significance or lack thereof in this specific scenario?

It could be argued that using the non-null assertion at the end of Angular's @Input properties might not be practical. What are your thoughts on this?

Update

Upon testing in a new Angular project, an error was encountered:

A definite assignment assertion '!' is not permitted in this context.ts(1255)

Based on this issue, it seems that including the ! operator on an @Input property may not be advisable. Refer to the screenshot for more information:

https://i.sstatic.net/8LwnI.png

javascriptangulartypescriptecmascript-6

Answer №1

By utilizing the strictPropertyInitialization compiler option, they ensure that any class property not declared with type undefined and not initialized directly or in a constructor will result in error TS2564.

https://i.sstatic.net/gmVNt.png

To address this compiler error, they apply the definite assignment assertion modifier, which informs TypeScript

...that a variable is indeed assigned for all intents and purposes, even if TypeScript’s analyses cannot detect so.

https://i.sstatic.net/sUk5b.png

Demo

For more information, visit:

In response to your update

You have failed to specify a type for the title variable in your example, leading to error TS1255. It is valid and logical to use ! in such scenarios!

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