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Assertion / Casting

Typescript

index.ts Raw #

// Casting = přetypování v TS nelze
// Asserce je explicitni určený typu

/*
  : = type annotation (deklarace typu)
  as / <> = type assertion (casting)
  <T> = generic type parameter (generika)
*/

// Oba tyto řádky dělají totéž - type assertion/casting
let value: any = "hello";
let length1 = (value as string).length;        // "as" syntax
let length2 = (<string>value).length;          // "angle bracket" syntax



/ 1. Type annotation
let myStr: string = "hello";

// 2. Type assertion (as) - když TS neví typ
let someValue: any = "hello";
let strLength = (someValue as string).length;

// 3. Type assertion (angle brackets) - stejné jako 2
let strLength2 = (<string>someValue).length;

// 4. Generic type parameter
let myObs: Observable<number>;


let x: unknown;
x = [];

// 1
let result = (x as number[]).push(111);

// 2
let result = (<number[]>x).push(111);