为什么javascript静态变量在不创建最少一个实例的情况下不能访问（使用类名）？

Question

I am creating one function like below

function calculation(){
    this.add=function(x,y){
        return x+y; 
    }   
    calculation.sub=function(x,y){
        return x-y; //static method
    };
    function mul(x,y){
        return x*y; //static method
    }
    calculation.mul=mul;
}

after declaration of this method, if call like this calculation.mul(2,1) I am getting an error like.

VM3676:1 Uncaught TypeError: calculation.mul is not a function at :1:13

But, var _calc=new calculation(); after creation of instance, I am able to access the static method.

calculation.mul(2,1) if i try after this, i am getting value `2`.

Anyone, please clarify me. Thanks, advance.

Answer 1

Because the code which assigns the mul property to the calculation object:

 calculation.mul=mul; 

… is inside the calculation function. Therefore it only runs when you call the calculation function.

Move it outside if you don't want it to work that way.

 function calculation() { this.add = function(x, y) { return x + y; } calculation.sub = function(x, y) { return x - y; //static method }; } function mul(x, y) { return x * y; //static method } calculation.mul = mul; console.log(calculation.mul(2, 1))