javascript - js object-oriented

Question

Excuse me, what is the difference between adding or not adding parentheses to the mm function after new? Why do I get the same results?
Please ask a senior expert to explain the principle inside.

Answer 1

First of all, for this kind of basic question, you need to learn to consult the official documentation.
The documentation has detailed instructions: new foo is equivalent to new foo(), which can only be used without passing any parameters.
Of course, you can’t completely trust the documentation. , after all, the pitfalls of js. .
Then what’s the difference? There are detailed descriptions in this
priority summary: new (with parameter list) has a priority of 19, and new (without parameter separation) has a priority of 18, so new foo() will be executed first

Finally, I remember seeing an article not long ago about a disgusting interview question, which was: new f(), new f, new f.g(), new f().g(), etc. Regarding the priority calculation problem, you can search it yourself

Answer 2

Refer to MDN

new constructor[([arguments])]

When there is no need to pass parameters, the brackets () are optional

Answer 3

var mm = function(val){

this.m = val

}
var a = new mm(1) ;
console.log(a)
var b = new mm ;
console.log(b)

Answer 4

If the constructor does not require parameters, there is no difference between adding and not adding parentheses.