MIT Weblab笔记 - Typescript

Introduction

TypeScript is a popular programming language that extends JavaScript by adding static types. Typescript catches errors at compile time rather than at runtime, making the code more reliable and easier to debug.

Syntax

Primitive Data Types

• number
• boolean
• string
• object
• undefined
• null

Declare a Type For a Variable

Define types of a variable using :.

let name: string = "John";
let age: number = 30;
let isStudent: boolean = false;

let message: string[] = ["1", "2", "3"];
let message: Array<string> = ["1", "2", "3"];

Define a Type

type Color = "Red" | "Green" | "Blue";
let c: Color = "Red"; // can only be one of three colors

type myType = {
    myProperty: string;
};

const newVariable: myType = {myProperty: "xxx"};

type User = {
    _id: string;
    name: string;
    is_admin?: boolean;
};

const user: User = {
    _id: "555";
    name: "Eric";
};

export {User}

• Denote optional params with ?

Typed Functions

const getComments = (id) => {
    return [];
}

const getComments = (id: string): Comment[] => {
    return [];
}

// add type for a function
type CommentProps = {
    _id: string;
    name: string;
    handleAdd: () => void;
}