Multiple types of functions

The first one is ：

function fun(n,m) {
    return n+m;
}
let return1 = fun(10,20)
let return2 = fun(100,200)
console.log(return1);
console.log(return2);

The second kind , Function declaration

let return1 = fun(100,200)
console.log(return1);

function fun(n,m) {
    return n+m;
}

The third kind of ： Anonymous functions , It's also called a callback function , Pass an anonymous function as a parameter to another function or method .

setInterval(function(){
    console.log("hello");
},1000)
//  It can be written like this 
function fun(){
    console.log("hello")
}
setInterval(fun,1000)

A fourth ： Function expression

const fun =function(n,m){
    return n + m;
}
let result = fun(10,22);
console.log(result);

The fifth ：

 Immediate execution function  , Code encapsulation 
 (function(){
    let a = 10;
     let b = 20;
     console.log(a + b);
 })()

6 kinds of ：

let str= "hello";
function fun1(){
    let str = "word";
    let num = 10;
    function fun2() {
    console.log(str);
    console.log(num);
    }
    fun2();
}
fun1 ();
console.log(str);

Seventh kinds ： Closure function code encapsulation

const module= (
    function(){
        let a = 10;
        let b = 20;
        function add(){
            return a+b;
        }
        return add;
    }) ()

Eighth ： Arrow function ：

Arrow function

const add= (x) => {

    return x * x;

}

In the second simplification

const add = x => x * x ;

 original 
const fun = function (x) {
    return x * x;
}
let result = fun(2);
console.log(result);

 The arrow function is abbreviated as ：

const fun =  (x) => {
    return x * x;
}
let result = fun(2);
console.log(result);

 More concise ：

const fun =  x=> {
    return x * x;
}
let result = fun(2);
console.log(result);

 The simplest ：

const fun =  x=>  x * x;
let result = fun(2);
console.log(result);

The arrow function has another this Pointing is more important ：

 primary ：
const cat = {
    name :"miaomiao",
    sangnn(){
        let self = this;
        window.setInterval(function(){
            console.log(self.name);
        },1000)
    }
}
cat.sangnn();
 After using the arrow ：

const cat = {
    name :"miaomiao",
    sangnn(){
        setInterval(() => {
            console.log(this.name);
        },1000)
    }
}
cat.sangnn();
 Arrow function and ordinary function this Point to different , A normal function refers to the object that calls the function .
 Where the arrow function is defined, it points to who .