Maximum size of an Array in Javascript

Question

Context  I m building a little site that reads an rss feed  and updates checks the feed in the background  I have one array to store data to display  and another which stores ID s of records that have been shown   Question  How many items can an array hold in Javascript before things start getting slow  or sluggish  I m not sorting the array  but am using jQuery s inArray function to do a comparison   The website will be left running  and updating and its unlikely that the browser will be restarted   refreshed that often   If I should think about clearing some records from the array  what is the best way to remove some records after a limit  like 100 items

User · Answer

I have shamelessly pulled some pretty big datasets in memory   and altough it did get sluggish it took maybe 15 Mo of data upwards with pretty intense calculations on the dataset  I doubt you will run into problems with memory unless you have intense calculations on the data and many many rows   Profiling and benchmarking with different mock resultsets will be your best bet to evaluate performance

User · Answer

You could try something like this to test and trim the length   http   jsfiddle net orolo wJDXL    x000D   x000D  var longArray    1  2  3  4  5  6  7  8   x000D   x000D  if  longArray length  gt   6    x000D    longArray length   3  x000D    x000D   x000D  alert longArray     1  2  3 x000D   x000D   x000D

User · Answer

I have built a performance framework that manipulates and graphs millions of datasets  and even then  the javascript calculation latency was on order of tens of milliseconds  Unless you re worried about going over the array size limit  I don t think you have much to worry about

User · Answer

No need to trim the array  simply address it as a circular buffer  index   maxlen   This will ensure it never goes over the limit  implementing a circular buffer means that once you get to the end you wrap around to the beginning again - not possible to overrun the end of the array    For example   var container   new Array     var maxlen   100  var index   0       store  1538 items  only the last  maxlen  items are kept  for  var i 0  i lt 1538  i         container  index     maxlen     storing    i        get element at index 11  you want the 11th item in the array  eleventh   container   index   11    maxlen       get element at index 11  you want the 11th item in the array  thirtyfifth   container   index   35    maxlen       print out all 100 elements that we have left in the array  note    that it doesn t matter if we address past 100 - circular buffer    so we ll simply get back to the beginning if we do that  for  i 0  i lt 200  i         document write  container  index   i    maxlen      lt br gt  n

User · Answer

Like  maerics said  your target machine and browser will determine performance  But for some real world numbers  on my 2017 enterprise Chromebook  running the operation  console time    Array x  fill 0  filter x   gt  x  lt  6  length console timeEnd      x 5e4 takes 16ms  good enough for 60fps x 4e6 takes 250ms  which is noticeable but not a big deal x 3e7 takes 1300ms  which is pretty bad x 4e7 takes 11000ms and allocates an extra 2 5GB of memory  So around 30 million elements is a hard upper limit  because the javascript VM falls off a cliff at 40 million elements and will probably crash the process   EDIT  In the code above  I m actually filling the array with elements and looping over them  simulating the minimum of what an app might want to do with an array  If you just run Array 2  32-1  you re creating a sparse array that s closer to an empty JavaScript object with a length  like  length  4294967295   If you actually tried to use all those 4 billion elements  you ll definitely your user s javascript process

User · Answer

It will be very browser dependant  100 items doesn t sound like a large number - I expect you could go a lot higher than that  Thousands shouldn t be a problem  What may be a problem is the total memory consumption

User · Answer

The maximum length until  it gets sluggish  is totally dependent on your target machine and your actual code  so you ll need to test on that  those  platform s  to see what is acceptable   However  the maximum length of an array according to the ECMA-262 5th Edition specification is bound by an unsigned 32-bit integer due to the ToUint32 abstract operation  so the longest possible array could have 232-1   4 294 967 295   4 29 billion elements

[javascript] Maximum size of an Array in Javascript

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