How is memory handled with javascript objects?

Question

Given:

Say an EventXObj is a javascript object that has many attributes and some methods.

An EventXObj can be associated to a simple string id as follows.

[ "id1" : Event1Obj , "id2": Event2Obj, ..., "id1000": Event1000Obj ]

And we want to represent how a single PlaceXObject can hold many events.

THE QUESTION:

In regards to below, does Scenario A take much more memory than Scenario B?

Scenario A

PlaceX.events = [ "id1", "id2", "id75", ... ]

Scenario B

PlaceX.events = [ Event1Obj, Event2Obj, Event75Obj, ... ]

Jakob · Accepted Answer · 2011-01-19 20:54:30Z

2

Scenario B is probably the most memory efficient one from a generic perspective. Everything in JavaScript is like a pointer/reference, so B uses a single integer (or so) for each event that is contained in your array.

Scenario A uses as much memory as your strings does, so for long string it would be bad. For your case, with very short strings, there is not much difference though.

answered Jan 19, 2011 at 20:54

Jakob

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1 Comment

b_dev Over a year ago

Thank you: This is what I really wanted to know, but I didnt know how to ask it ---> "Everything in JavaScript is like a pointer/reference"

jweyrich · Accepted Answer · 2011-01-19 21:09:57Z

2

It depends exclusively on the memory model used by the JavaScript engine you're using.

Taking the current version of V8 as example (assuming 32 bit):

Pointers = 4 bytes.
Strings = 12 + [string length] bytes.
Concatenated strings = 12 + 2 * 4 bytes (2 * 4 because it's a pair of pointers to existing strings). However, you can force flat-strings if you want.
Dictionary with n elements = 3 * 4 * 2 * closestPowerOfTwo(n) bytes.

Now you're able to do the math for the current version of V8.

answered Jan 19, 2011 at 21:09

jweyrich

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