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TS initial use, TS type
2022-07-01 23:34:00 【qq_ forty-six million three hundred and two thousand two hundre】
ts Type statement
// Parameters a,b, The type of the return value of the function is declared as number type , If there is a non in the transmission parameter number Data of type , A red wavy line will be displayed
function sum(a: number, b: number): number {
return a + b
}
console.log(sum(1, 9)); //10
// Here a amount to const Defined ,a The value of is always 10
let a: 10;
//b The value of can only be 'male' perhaps 'female'
let b: 'male' | 'female'
//b The value of can only be boolean Type or string type
let c: boolean | string
//any Represents any type of , You can give d Assign any type of value ( It's equivalent to d Shut down the TS Type detection of )
let d: any
d = true
// Equate to let d
let s: string
s = d // d yes any type ,s Also became any type ( So try to avoid using any)
//unknown Indicates an unknown type , You can also give d Assign any type of value
let e: unknown
e = 'hellow'
let s: string
//s = e // Grammar detection failed , because s yes string type ,e yes unknown type , Their types are different , Direct assignment is not allowed
// If you just want to e The value is assigned to s, There are two solutions
Method 1 :
if(typeof e === "string") {
s = e
}
Method 2 :
// Use type assertion
s = e as string
perhaps :
s = <string>e
// void It is used to express empty , Take functions for example , It means that there is no return value
function fn(): void {
}
function fn(): void {
//return undefined
//return;
//return null
}
Once the function reports an error, it immediately terminates ,never Rarely used
// {} Used to specify the object type
let a: {
name: string}
// a There are and only name attribute , And name Value must be string type
a = {
name: ' Pig eight quit '}
let b: {
name: string, age?: number}
// b There must be name attribute , And name Value must be string type ;age not essential ;
b = {
name: ' Pig eight quit '}
perhaps
b = {
name: ' Pig eight quit ', age: 18}
let c: {
name: string, [propName: string]: number}
// b There must be name attribute , And name Value must be string type ; Number of remaining attributes , Attribute names are not required , But it must be number type
c = {
name: ' Pig eight quit ', haha: 12, xixi: 99}
// () => {} Used to specify the function object type
let d: (a: number, b: number)=>number
// function d Only two are received number Parameters of type , And the return value must be number type
d = function(n1: number, n2: number): number {
return n1 + n2
}
// [] Used to specify the array type
let a: number[]
Equate to
let a: Array<number>
a = [1,3,6,5,9]
//tuple Is a tuple (ts newly added ), Tuples represent fixed length arrays
let a: [string, number]
// Array a There are only two elements in it , The first is string type , The second is number type
a = [1, '2']
//enum Is the enumeration (ts newly added )
enum Gender{
male,
female
}
let a: {
name: string, gender: Gender}
a = {
name: ' Pig eight quit ', gender: Gender.male}
// & Indicates simultaneous
let a: {
name: string} & {
age: number}
Equate to
let a: {
name: string, age: number}
// object a There must be both name and age, And the type is the specified type
a = {
name: ' Pig eight quit ', age: 18}
// Alias for type
type myType = 1 | 2 | 3
let a: myType
let c: mType
a = 1, c = 3
// a、c The value of is 1 or 2 or 3, Will do
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