Bang colon notation in Angular is a powerful feature that allows developers to interact with

Question

Bang colon notation in Angular is a powerful feature that allows developers to interact with

While browsing through the Angular Deprecation docs, I stumbled upon the use of `!:` notation.

@Input() tpl !: TemplateRef<any>;
@ContentChild(TemplateRef) inlineTemplate !: TemplateRef<any>;

This same notation was also found here as well.

@Input() id !: string;

The meaning or concept behind the `!:` notation in Angular is unclear to me. My attempts to find information through Google, SymbolHound, and Angular Docs have not been successful.

If anyone could provide insight into how it functions, or share a documentation link, it would be greatly appreciated.

angular typescript

Answer 1

Answer №1

When using strictNullChecks, decorating something with @Input can lead to complaints in TypeScript. For instance...

public class MyComponent {

  @Input()
  public myField: string;

  constructor() {}

}

This will trigger TypeScript errors because myField is not declared as nullable, so it should never be assigned a value of null or undefined. Since it's also not initialized in the constructor, its initial value will be undefined.

However, we know that Angular will eventually assign a value after construction. If we make the field nullable like public myField: string?, we'll have to handle countless this field may be null errors.

As a workaround, we use a ! on the field declaration to assure TypeScript that even though it seems like it could be initialized to null/undefined, we will manage it properly.

Answer 2

When using strictNullChecks, decorating something with @Input can lead to complaints in TypeScript. For instance...

public class MyComponent {

  @Input()
  public myField: string;

  constructor() {}

}

This will trigger TypeScript errors because myField is not declared as nullable, so it should never be assigned a value of null or undefined. Since it's also not initialized in the constructor, its initial value will be undefined.

However, we know that Angular will eventually assign a value after construction. If we make the field nullable like public myField: string?, we'll have to handle countless this field may be null errors.

As a workaround, we use a ! on the field declaration to assure TypeScript that even though it seems like it could be initialized to null/undefined, we will manage it properly.

Answer 3

Answer №2

In programming, the exclamation mark ! indicates that a field is both non-null and non-undefined (refer to Google's TypeScript documentation for more information).

On the other hand, the colon : serves as a simple separator between the field name and its type.

Answer 4

In programming, the exclamation mark ! indicates that a field is both non-null and non-undefined (refer to Google's TypeScript documentation for more information).

On the other hand, the colon : serves as a simple separator between the field name and its type.

Bang colon notation in Angular is a powerful feature that allows developers to interact with

Answer №1

Answer №2

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