Can you explain the significance of the symbol ! when declaring a variable in TypeScript?

Currently, I am delving into an Angular project and came across a peculiar line of code in the component.ts file provided by my instructor.

@Input() public searchType!: string;

This line resides within the OnInit() function of the component's TypeScript. However, the exclamation mark '!' is throwing me off - what significance does it hold in this context? In other programming languages like PHP or Java, it typically symbolizes inequality, but its role seems different here when initializing a variable in TypeScript.

angulartypescript

Answer №1

! - also known as TypeScript's non-null assertion operator, is a method to explicitly declare to typescript that you are certain the value of a property is not null or undefined.

It is important to note that using this operator can be risky, as unexpected behavior may occur if the value does turn out to be null or undefined. In essence, this allows you to "quiet down" typescript, and should only be utilized when you are completely confident in its appropriateness for your specific scenario.

Contrary to JavaScript's ?, which represents the optional-chaining operator, indicating that the value could potentially be undefined, resulting in a return of undefined in such situations.

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