Javascript函数的所有参数是否仅按值传递？

Question

If I have a variable like this:

I created something similar to an ENUM like this:

 var ContentStatusId = {
        All: 0,
        Production: 1,
        Review: 2,
        Draft: 3,
        Concept: 4
    }

When I call a function like this:

doTask(myParam) {
    var a = 
}

With doTask(ContentStatusId.All);

Is there any way that I can find out anything about the parameter passed to the function or is it completely passed by value only? Are there any other ways to pass parameters to a function?

Answer 1

In JavaScript all parameters are passed by value.

In the case of a primitive, the value is the primitive value.

function test(arg) {
  console.log(arg);
}
test(1);

arg will have the value of 1.

However, if you say

test({});

then arg will contain a value which is a REFERENCE to the object we just created.

Edit to address comment

You can do...

doTask(myParam) {
  if (myParam === ContentStatusId.Review) {
   // Do stuff
  }
}

doTask(ContentStatusId.Review);

or

doTask(myParam) {
  switch(myParam) {
     case ContentStatusId.Review:
     // Do stuff
     break;
  }
}

Answer 2

There is nothing calling pass by reference in javascript.

Everything gets passed by value only .

Eg

If in case of primitive value

eg

var a = 10;

console.log(a); // 10

fun xyz(a); // passing a 

function xyz(a) {
    a += 10;
    console.log(a); // 20
} // function will receive the value. If you modify it, It will still will not be reflected back to what you passed

console.log(a); // 10

Other way round,

When you pass object to a function, The references gets copied.

eg

var obj = { 'a': 10 };

console.log(obj.a); // 10

function xyz(obj) {
    obj.a = obj.a + 10;
    console.log(obj.a); // 20
} // here the obj will be copied as reference. So when you modify it, It will get reflected back to original object.

console.log(obj.a); // 20