I've noticed this popping up in a few spots lately, but I haven't been able to find any information about it.
I'm intrigued by the use of the '!' symbol in Angular syntax. Can anyone explain what it does?
I've noticed this popping up in a few spots lately, but I haven't been able to find any information about it.
I'm intrigued by the use of the '!' symbol in Angular syntax. Can anyone explain what it does?
According to the Angular documentation:
The non-null assertion operator ( ! )
In Typescript 2.0, strict null checking can be enforced using the
--strictNullChecksflag. This ensures that variables are not unintentionally assigned asnullorundefined.Under this mode, typed variables by default do not allow
nullorundefined. The type checker will generate an error if a variable is left unassigned, or ifnullorundefinedare assigned to a variable that does not permit these values.The type checker will also throw an error if it cannot determine whether a variable may be
nullorundefinedat runtime. Even if you know it's impossible, the type checker may not. You can clarify this to the type checker with the post-fix non-null assertion operator (!).The Angular non-null assertion operator (!) fulfills a similar role within an Angular template.
For instance, after ensuring that
herois defined using*ngIf, you can assert that the properties ofheroare also defined.<!-- No hero, no text --> <div *ngIf="hero"> The hero's name is {{hero!.name}} </div>By converting your template into TypeScript code, the Angular compiler prevents TypeScript from raising concerns about
hero.namepotentially beingnullorundefined.Unlike the safe navigation operator, the non-null assertion operator does not offer protection against
nullorundefined. Instead, it informs the TypeScript type checker to temporarily suspend strict null checks for a specific property expression.This template operator becomes essential when activating strict null checks but remains optional otherwise.
This feature is known as the "Non-null assertion operator" and it is not directly related to Angular, but rather a part of TypeScript itself.
let s = e!.name; // Asserting that e is non-null before accessing name
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