Can I pass parameter like reference

Question

I need function change to change variables and return back to Tst1. I expect to get in console:

5
aaa

but have unchanged ones:

6
bbb

My functions:

function change ( aa,bb )
{
    aa=5;
    bb="aaa";
}

function Tst1() 
{
    aa=6;
    bb="bbb";
    change(aa,bb);

    console.log (aa);
    console.log (bb);
}

Have a look at this answer http://stackoverflow.com/a/13104500/57095 — Alberto Zaccagni, Nov 19 '15 at 11:50
You can declare those variables as global ones. Demo: https://jsfiddle.net/b9Ljkq8g/ — Werner, Nov 19 '15 at 12:01

score 3 · Answer 1 · answered Nov 19 '15 at 12:11

One way is to move change() into the function test(). Then it shares the same variables as the calling scope.

'use strict';

function test() {

    function change() {
        aa = 6;
        bb = 76;
    }

    var aa = 5,
        bb = 6;
  
  change();      
  document.write(aa + "   " + bb);
}
test();

score 1 · Accepted Answer · answered Nov 19 '15 at 11:55

JavaScript is like java in that primitives are never passed by reference but objects are always passed by reference. You need to wrap your data in an object and pass that instead:

function change (aa, bb)
{
    aa.value = 5;
    bb.value = "aaa";
}

function Tst1() 
{
    aa = { value: 6 };
    bb = { value: "bbb" };
    change(aa, bb);

    console.log (aa.value); // outputs 5
    console.log (bb.value); // outputs aaa
}

score 1 · Answer 3 · answered Nov 19 '15 at 12:00

1

or you can play with global variable, but it is not a good practice.

var aa,bb;

function change(){
  aa=6;
  bb=76;
}

function test(){

  aa = 5;
  bb = 6;
  
  change();
  
  console.log(aa + "   " + bb);
}

test();

answered Nov 19 '15 at 12:00

Shubham

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score 0 · Answer 4 · edited Nov 19 '15 at 12:36

0

Short answer: NO, you can't pass primitive parameters by reference in JS.
One alternative solution to the presented here is to return the result values as array of items:

 
function change ( aa,bb )
{
    aa=5;
    bb="aaa";
    return [aa, bb];
}

function Tst1() 
{
    aa=6;
    bb="bbb";
    result = change(aa,bb);
    aa = result[0];
    bb = result[1];

    document.writeln(aa);
    document.writeln(bb); 
}

Tst1();

edited Nov 19 '15 at 12:36

Danield

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answered Nov 19 '15 at 12:06

d.raev

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Useful sometimes, yes. But not when the question is specifically about parameter passing and mutating those parameters. – James Thorpe Nov 19 '15 at 12:10

Can I pass parameter like reference

4 Answers4