Storing in javascript array vs. (LocalStorage and IndexDB)

Question

How is storing values directly in Javascript arrays is different than from storing them in come client side alternative like LocalStorage or IndexDB.

Where the values get stored in either cases. And what are limits.

My use case is: to store very fast data (float values) coming from server somewhere and then read it from that middle source to render the points on a real time plot/graph. Does the frequency also makes a difference to the choice ?

Any sample code snippet will be of great use.

You will most certainly be optimizing the rendering of data and possibly the client-side processing. That is your main bottlenecks, not the storage itself. — David Hellsing
– David Hellsing, Commented Oct 7, 2012 at 9:40

Denys Séguret · Accepted Answer · 2013-03-02 08:06:08Z

4

Obvious differences between localStorage and arrays are :

you can only store strings (no objects)
it's persisted so that you'll get your values back next time
as it writes on disk it's a heavier operation
the available space is limited to avoid cluttering the user's disk ("User agents should limit the total amount of space allowed for storage areas.[...] A mostly arbitrary limit of five megabytes per origin is recommended")

W3.org reference on localStorage

You read and write in localStorage like this :

var foo = localStorage["bar"];
// ...
localStorage["bar"] = foo;

(example taken from the great introductory site http://diveintohtml5.info/storage.html)

If you're only using your data for the current session, don't use localStorage. Use standard arrays (they're fine and fast) or Float32Array.

edited Mar 2, 2013 at 8:06

answered Oct 7, 2012 at 9:33

Denys Séguret

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12 Comments

David Hellsing Over a year ago

Why not use getItem() and setItem() methods instead?

Andy897 Over a year ago

Thanks a lot for reply. But my doubt goes unresolved. So, I have to store few thousand float values every second. And I want to store these for 2 minutes and discard values which are older than that. So, what is the right way ? Any harm in plainly storing them in a javascript array ? so it will be like 500kbps of data => 50-60 mb for 2 minutes.

Andy897 Over a year ago

Hi David, thanks for comment. Can you please elaborate a bit.

Denys Séguret Over a year ago

@David because the brace notation is cleaner and prettier... but you may if you want use getItem and setItem.

Denys Séguret Over a year ago

@user969107 There is no point in using localStorage to store data only for current session.

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