你听过js中函数执行吗

function demo_one(){
console.log("this is demo-one");
 }

var demo=function(){
  console.log("this is demo-two");
   }

function(){
    console.log("this is demo-three");
 }
 var name="maomin";
  function main(){//这里是声明一个叫mian函数,简单的叫做函数体，现在还不是函数表达式。
  console.log(this.name);//输出 maomin 
 }
main();

var main=function(){
  console.log(this.name);//输出maomin，这里是函数表达式。
 }
main();

!function main(){
  console.log("this is !");
 }();
// or
!function(){
  console.log("this is wuming");
   }

(function(age){
  console.log(age);
 })(21);
// or
(function(money){
  console.log(money);
 }(100));

var a=document.querySelector("body");
 a.onclick=function(){
  alert("被点击了！")
 }
 var time=setInterval(function(){
  var name="maomin";
  console.log(this.name)
 },2000)