function
function type
define a type for the function
function add (x: number, y: number): number {
return x + y}
ts can automatically infer the return type from the return statement, so we usually omit it.
Expression functions (anonymous functions)
const add:(x:number, y:number) => number = function(x,y) {
return x + y}
Contains parameter types and return value types.
If the function does not return any value, the return value type must be specified
voidand cannot be left blank.
inferred type
If the anonymous function parameter in the above expression function does not specify a type, the typeScript compiler will automatically recognize the type
This is called "categorization by context" and is a type of type inference.
Optional parameters and default parameters
Every function parameter in ts is required. The compiler checks that the user has not entered a value for each parameter.
function add (a:string,b:number){
}
add('1')//error
add('1',1,1)//error
add('1',1)
Implement optional parameter functions
Beside the parameter use？
Optional parameters must come after required parameters
function add (a:string, b?:number) {
}
provide a default value
function add (a: string, b: number = 1) {
}
add('1')
add('1',1)
add('1',1,1)//error
Parameters with default values do not need to be placed after required parameters
remaining parameters
function add (a:string, ...restArgs:any[])
There can be none, or any number.
this parameter
I don't understand, I don't see it at first glance
overload
not at first glance