Do object references take up extra memory?

Question

Lets say you have the following complex object:

var object1 = .... // (something complexed)

This takes up x amount of memory in your JS application. Now lets say you have some other objects that reference object1:

var otherObject = { something: true, value: 'yes', object: object1 };

var anotherObject = { color: '#FFF', object: object1 };

Have I tripled the amount of memory that object1 originally took up? Or do the references to object1 not add to the overhead of the memory used?

I'm not sure how to test this myself in order to determine the answer. (Bonus points if you can tell me how to point me to a tool that helps benchmark this).

Well, you'd need some memory to indicate that the reference does exist. Otherwise, how'd you know if it's there or not. — Joseph, May 28 '13 at 04:21

score 9 · Accepted Answer · edited May 23 '17 at 11:45

9

Objects are always passed by reference in JavaScript (see this popular answer). Pointer to an object takes some amount of memory (depends on implementation), of course, but much less than the actual object.

edited May 23 '17 at 11:45

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answered May 28 '13 at 04:24

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score 7 · Answer 2 · edited May 23 '17 at 12:00

Take a look at this question. Numbers, strings, etc. are always called by value, but objects are called by sharing; that is they are called by value, but the value is a reference to the object.

In other words, if you modify the pointer's properties, you are modifying the same pool of memory as the object. But if you reassign the pointer, it does not affect the original object.

What this means is that, in your example, you have not tripled the amount of memory that object1 took up, but the extra pointers to object1 will take up some memory space. Exactly how much space? That depends on the precise implementation of the Javascript engine, but it will always be much less than the size of the object.

As far as benchmarking goes, look at Mozilla's documentation for their JS engine, SpiderMonkey. There are lots of good utilities there....

Do object references take up extra memory?

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