Pointers in JavaScript?

Question

Can we pass a reference of a variable that is immutable as argument in a function?

Example:

var x = 0; function a(x) {     x++; } a(x); alert(x); //Here I want to have 1 instead of 0 

Answer 1

Since JavaScript does not support passing parameters by reference, you'll need to make the variable an object instead:

var x = {Value: 0};    function a(obj)  {      obj.Value++;  }    a(x);  document.write(x.Value); //Here i want to have 1 instead of 0

In this case, x is a reference to an object. When x is passed to the function a, that reference is copied over to obj. Thus, obj and x refer to the same thing in memory. Changing the Value property of obj affects the Value property of x.

Javascript will always pass function parameters by value. That's simply a specification of the language. You could create x in a scope local to both functions, and not pass the variable at all.

Answer 2

This question may help: How to pass variable by reference in javascript? Read data from ActiveX function which returns more than one value

To summarise, Javascript primitive types are always passed by value, whereas the values inside objects are passed by reference (thanks to commenters for pointing out my oversight). So to get round this, you have to put your integer inside an object:

var myobj = {x:0};    function a(obj)  {      obj.x++;  }    a(myobj);  alert(myobj.x); // returns 1