Basic type variable declaration

One , Preface

1. be relative to javascript,typescript One of the characteristics of can Declare variables with data types .

2. When a variable with a confirmed data type is assigned a value of a different type , It will be wrong when compiling , To some extent, it can typescript Understood as strongly typed javascript

Two , The form of the statement

1.let [ Variable name ] : [ type ] = value perhaps let [ Variable name ] : [ type ]

let a:number = 10
let b:string

2. Declare the type of the variable , But there is no initial value , The variable value will be set to undefined

3、 ... and , Legal base types

1. Any type ：any

let a:any = 'hello world'
a = 123 // If the assignment is of different types, no error will be reported 

2. Numeric type ：number

let a:number = 123
let b:number = 0b1010

3. String type ：string

let a:string = "123"

4. Boolean type ：boolean

let a:boolean = true

5. An array type ：[ type ][] || Array< type >

let a:any[] = [1,"2",true]
let b:Array<number> = [1, 2, 3]

6. object type ：object

let a:object = [1,"2",true]
let b:object = {
    a:1}

7.null and undefined, stay ts in ,undefined and null They have their own types called undefined and null, It's not very useful in itself

let a:undefined = undefined
let b:null = null

8. Tuples

9. enumeration

10.void