Question

I don’t understand the assignment operator when assigning objects (say, arrays). I’m told that as assignment operator copies the reference. However it seems like it copies the data. For example:

var globArray = [];

function test() {
  var names = ["craig", "silva"];
  globArray = names;
}//endFunction test

function test2() {
  console.log("el1: ", globArray[0], "el2: ", globArray[1]);
}//endFunction test2

When I call TEST, it creates array NAMES and assigns the global array “globArray” to NAMES. Now it goes out of scope, so “names” is gone, right? Then later I call test2, but it DOES show the elements! So it must have COPIED the whole object, as opposed to just coping the reference.

Can someone explain this?

Answer 1

When your “test” function returns, you’re correct that “names” is “gone”. However, its value is not, because it’s been assigned to a global variable. The value of the “names” local variable was a reference to an array object. That reference was copied into the global variable, so now that global variable also contains a reference to the array object.

Object allocation is a global thing. When an object is allocated and referenced by a local variable, then it will be garbage-collected when the local variable disappears when its scope becomes inactive unless some other reference (direct or indirect) to the object exists. A direct reference would be a case like yours. An indirect reference can happen if the local scope “leaks” a function that includes a reference to the local variable.