Multiple definitions and calling methods of functions

1. How the function is defined

(1) Function keyword (named function)

function fn(){
    
     }

(2) Function expression (anonymous function)

let fun=function(){
    
    }

（3）new Function()

let fn=new Function('参数1','参数2','函数体');
fn();

• The functions in Function must be in string format
• The third method is inefficient and less used
• All functions are instance objects of Function
• Functions are also objects

2. How to call the function

(1) Ordinary function

function fn(){
    
    
		console.log(1);
		}
fn();
fn.call();

(2) Object method

let o={
    
    
	sayHi:function(){
    
    
			console.log(1);
			}
	}
o.sayHi();

(3) Constructor

function Star(){
    
     }
new Star();

(4) Binding event function

btn.onclick=function(){
    
    }
//触发

(5) Timer function

setInterval(function(){
    
    },1000)
//时间触发 一秒钟触发一次

(6) Execute the function immediately

(function(){
    
    
	console.log(1)})();
//自动调用