js中构造函数的输出

function Demo(){
    this.fn=function(){
        console.log(1)
    } 
}

Demo.fn=function(){
    console.log(2)
}
Demo.prototype.fn=function(){console.log(3)}
function fn(){
    console.log(4)
}
var fn=function(){
    console.log(5)
}
// Demo.fn()//2
// Demo.fn//不执行
// Demo().fn()//报错

// console.log(Demo.fn())
/* 
    2
    undefined
*/
// console.log(Demo.fn)
/* 
    ƒ (){
        console.log(2)
    }
*/
// console.log(Demo().fn())
/*
    Uncaught TypeError: Cannot read properties of undefined (reading 'fn')
*/


// new Demo().fn()//1
// new new Demo().fn()//1
// new Demo.fn()//2
// new new Demo.fn()
/* 
    2
    Uncaught TypeError: (intermediate value) is not a constructor
*/

// console.log(new Demo().fn())
/* 
    1
    undefined
*/
// console.log(new new Demo().fn())
/* 
    1
    Demo.fn()
*/
// console.log(new Demo.fn())
/* 
    2
    Demo.fn()
*/
// console.log(new new Demo.fn())
/* 
    2
    报错
*/

// fn()//5