typescript-for-js-programmer

• [Engineering] Typescript for JS Programmer
  • Type by Inference: TS will define type of a variable by assigned value
  • Interfaces vs Types: using interface to define type
  • Unions: a variable can have multiple types

      function getLength(obj: string | string[])
    

  • Generics: can use Type as generic Type and assign a specific type to Type in declare

      interface Container<Type> {
        push: (obj: Type) => void;
        pop: () => Type;
      }
    
      declare const stringContainer: Container<string>;
      stringContainer.push("abc");
    

  • Duck Typing = Structural Typing = shape-matching:

      interface Point {
        x: number;
        y: number;
      }
    
      const point = { x: 1, y: 2 }; // auto match to Point type
      const rect = { x: 1, y: 2, width: 10, height: 30 }; // auto match to Point type (kind of casting to Point)
      const color = { hex: "#FFFFFF" }; // failed-matched to Point type