Typescript raw data type

data type

summary

• The type declaration is TS A very important feature
  • Type declarations allow you to specify TS Medium variable （ Parameters 、 Shape parameter ） The type of
  • After specifying the type , When assigning a value to a variable ,TS The compiler will automatically check whether the value conforms to the type declaration , If yes, the value is assigned , Otherwise, the report will be wrong
  • In short , The type declaration sets the type... For the variable , So that variables can only store certain types of values

• TypeScript There are two types of data in
  • Raw data type （ Basic data type ）
  • object type （ Complex data type ）
• Common basic data types ：number / string / boolean / undefined / null
• Automatic type determination
  • TS Have automatic type judgment mechanism
  • Simultaneous declaration and assignment of variables ,TS The compiler determines the type of variable
  • So if you declare and assign variables at the same time , You can omit the type declaration

type

type	Example	describe
number	1,-2,3.4	Arbitrary number
string	"hi",'hi',hi	Any string
boolean	true、false	Boolean value true or false
Literal	Its own	Limiting the value of a variable is changing the literal value
any	*	Any type
unknown	*	Type safe any
void	Null value （undefined）	No value （ or undefined）
never	No value	Cannot be any value
object	（name: ' ROM. '）	Any of the js object
array	1, 2, 3	Any of the js Array
tuple	4, 5	Tuples ,TS New type , Fixed length array
enum	enum(A, B)	enumeration ,TS New type in

stay ES6 and ES10 New basic data types are introduced in , Namely Symbol and BigInt

Raw data type

Numeric type

Use keywords number Define the number type

let decimal: number = 6.1; //  decimal 

let hex: number = 0xf00d; //  Hexadecimal 

let binary: number = 0b1010; //  Binary system 

let octal: number = 00744; //  octal 

let big: bigint = 100n;

String type

Use keywords string Define string type

let color: string = 'bule';
color = 'red';

let fullName: string = 'Law D';
let age: number = 12;
let sentence: string = `Hello, my name is ${fullName}.I am ${age} years old.`
//  among  ``  Used to define  ES6  Template string in , Its effect is equal to 
let sentence: string = 'Hello, my name is' + fullName + '.I am' + age + 'years old.'

Boolean type

Use keywords boolean Define Boolean types

let isDone: boolean = false;

notes ： Non strict mode number、string、boolean All values can be empty

Void type

stay TypeScript in , It can be used void Represents a function that does not have any return value

function hello(): void {
    alert("Hello TS");
}

let unuseable: void = undefined; //  Declared but unassigned variable values （ Value not found ）

Null type

Indicates that the object is missing

let nu: null = null; //  Declared and assigned （ Can find , The value is null）

Undefined type

Used to initialize a variable to an undefined value

let un: undefined = undefined;

• void and undefined The difference between

let un: undefined;
let num: number = un; //  Can be  undefined  A variable of type is assigned to  number  Variable of type 

let vo: void;
let num: number = vo; // void  Variables of type cannot be given to  number  Variable assignment of type 

undefined and null Is a subtype of all types