Question

I have a global variable MyGlobalVar and some code that looks like this:

var MyGlobalVar = null;

function PlayWithMyGlobal() {
    MyGlobalVar = new Object();
    .... adding properties to MyGlobalVar
    MoreFun(MyGlobal);
}

function MoreFun(TheVar) {
    is TheVar here a local or just a reference to the global?
} 

If I pass the global variable, am I still working with the global?
Thanks.

Answer 1

If the global variable is an object, then you’re still working with the global variable. Otherwise, it’s a copy.

As shown and annotated below, your variables point to the same global object.

var MyGlobalVar = null;

function PlayWithMyGlobal() {
    MyGlobalVar = new Object(); // <--- Object
    MoreFun(MyGlobalVar); // <--- Passing object reference
}

function MoreFun(TheVar) {
    TheVar.test = 'Did I modify global?';
    alert(TheVar === MyGlobalVar); // true
    alert(MyGlobalVar.test);       // "Did I modify global?"
}