Learn typescript (1)

Why use  typescript

The program is easier to understand

• problem ： Input and output parameter types of functions or methods , External conditions, etc

• Constraints of dynamic language ： Manual debugging and other processes are required

• With Typescript： The code itself can answer the above questions

Fewer mistakes

• Most errors can be found during compilation

• Put an end to some common mistakes

Very good inclusiveness

• Fully compatible with  Javascript

• Third party libraries can write type files separately

• Most projects support  typescipt

A little flaw

• Increased some learning costs

• Some development costs have been increased in the short term

data type

Raw data type

let isDone: boolean = false

let age: number = 10

let firstName: string = 'viking'
let message: string = `Hello, ${firstName}`

let u: undefined = undefined
let n:null = null

let num: number = undefined


Any type

let notSure: any = 4
notSure = 'maybe a string'
notSure = true

notSure.myName
notSure.getName()


Arrays and tuples

Array

let arr: number[] = [1,2,3]
arr.push(3)

// arguments An array of class  IArguments type , No Array
function test(){
 console.log(arguments);
 arguments.length
 arguments[0]
}


Tuples

Put elements of different data types together

let user: [string, number] = ['abc', 20]
user.push('1212') Can only push Existing types


Interface  Interface

interface IPerson{
 readonly id: number; //  Read-only property
 name: string
 age: number
 address?: string //  Optional attribute
}

let lihua: IPerson = {
 id: 1,
 name: 'lihua',
 age: 20
}


function

function add(x: number, y: number, z?: number): number {
 if (typeof z === 'number') {
 return x + y + z
 } else {
 return x + y
 }
}
add(1, 2)
add(1, 2, 3)

const add = (x: number, y: number, z?: number): number => {
 if (typeof z === 'number') {
 return x + y + z
 } else {
 return x + y
 }
}

interface ISum{
 (x: number, y: number, z?: number):number
}
let add2: ISum = add