TypeScript 001: Basic Types

最近开始学习TypeScript的一些随手笔记,年纪大了怕忘了。

Basic Types

  • Boolean

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    let isDone: boolean = false;
  • Number

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    let decimal: number = 6;
  • String

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    let fullName: string = `Bob Dylan`
    let sentence: string = "Hello, my name is " + fullName + ".\n\n" + "I'll be " + (age + 1) + " years old next month."
  • Array

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    let list: number[] = [1, 2, 3];
    let list: Array<number> = [1, 2, 3];
  • Tuple

    • array with a fixed number of elements whose types are known
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    let x: [string, number]    // order matters
  • Enum

    • enums begin numbering their members starting at 0
    • you can go from a numeric value to the name of that value in the enum
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    enum Color {Red, Green, Blue}
    let c: Color = Color.Green;
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    enum Color {Red = 1, Green, Blue}
    let colorName: string = Color[2]

    console.log(colorName); // Green
  • Any

    • describe the type of variables that we do not know when we are writing an application
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    let notSure: any = 4;
    notSure = "maybe a string instead"
    notSure = false;
  • Void

    • the absence of having any type at all
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    function warnUser(): void {
    console.log("This is my warning message")
    }
  • Null and Undefined

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    let u: undefined = undefined;
    let n: null = null;
  • Never

    • represents the type of values that never occur
    • the return type for a function expression that always throws an exception or one that never returns
    • the never type is a subtype of every type
    • no type is a subtype of never
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    function error(message: string): never {
    throw new Error(message)
    }
  • Object

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    declare function create(0: object | null): void;

    create({ prop: 0 });
  • Type assertions

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    let someValue: any = "this is a string";
    let strLength: number = (<string>someValue).length
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    let someValue: any = "this is a string";
    let strLength: number = (someValue as string).length