Does JavaScript pass by reference? [duplicate]

Answer 1

Objects are always pass by reference and primitives by value. Just keep that parameter at the same address for objects.

Here's some code to illustrate what I mean (try it in a JavaScript sandbox such as https://js.do/).

Unfortunately you can't only retain the address of the parameter; you retain all the original member values as well.

a = { key: 'bevmo' };
testRetain(a);
document.write(' after function ');
document.write(a.key);


function testRetain (b)
{
    document.write(' arg0 is ');
    document.write(arguments[0].key);
    b.key = 'passed by reference';
    var retain = b; // Retaining the original address of the parameter

    // Address of left set to address of right, changes address of parameter
    b = {key: 'vons'}; // Right is a new object with a new address
    document.write(' arg0 is ');
    document.write(arguments[0].key);

    // Now retrieve the original address of the parameter for pass by reference
    b = retain;
    document.write(' arg0 is ');
    document.write(arguments[0].key);
}

Result:

arg0 is bevmo arg0 is vons arg0 is passed by reference after function passed by reference