Understanding Memory Management in JavaScript, Mozilla

Question

I'm new to JavaScript and trying to understand the memory management related to objects using this Mozilla reference: MDN Memory Management.

I am following an example, but having issues in understanding the references.

var o = { a: { b:2 } }; // 2 objects are created. One is referenced by the other as one of its property. // The other is referenced by virtue of being assigned to the 'o' variable. // Obviously, none can be garbage-collected var o2 = o; // the 'o2' variable is the second thing that // has a reference to the object o = 1; // now, the object that was originally in 'o' has a unique reference // embodied by the 'o2' variable var oa = o2.a; // reference to 'a' property of the object. // This object has now 2 references: one as a property, // the other as the 'oa' variable o2 = "yo"; // The object that was originally in 'o' has now zero // references to it. It can be garbage-collected. // However what was its 'a' property is still referenced by // the 'oa' variable, so it cannot be free'd oa = null; // what was the 'a' property of the object originally in o // has zero references to it. It can be garbage collected.

I got confused by terms like this object, one is referenced by the other, 2 objects are created - for what? 'o' & 'a'?, that has a reference to the object - which object?

Can someone rephrase the comments above with the actual object names, please?

It may consider as a spoonfeeding question but let me know if it's not worth to ask this question. I'll delete it.

Objects don't have names; that's kind of the point. There are either variables (or object properties) referencing an object or there aren't. — Pointy
– Pointy, Commented Sep 4, 2014 at 20:19
JavaScript has literal notation for objects. These objects can have other objects as their properties. — PM 77-1
– PM 77-1, Commented Sep 4, 2014 at 20:20

Lucas Ross · Accepted Answer · 2014-09-04 20:40:12Z

It is a bit of a crummy explanation. I'll give you a rough edition.

var o = { a: { b:2 } }; // 2 objects are created. One (the value of the property named "a") // is referenced by the other (the value of the variable named "o") // as its property. // The other (the value of the variable named "o") // is referenced by virtue of being assigned to the 'o' variable. // Obviously (maybe to the author...), none can be garbage-collected var o2 = o; // the 'o2' variable now also // has a reference to the object (the value of the variable "o") o = 1; // "o" now refers to something else and "o2" is the only variable // referring to the original "o" object. var oa = o2.a; // reference to the 'a' property of the "o2" object. o2 = "yo"; // The object that was originally in 'o' has now zero // references to it, but // the object's 'a' property is still referenced by // the 'oa' variable, so the "o2" object cannot yet // be GC'ed. oa = null; // The object now has zero references to it, so it can be // garbage collected.

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