#98 new

Autocomplete poor performance on large lists

Reported by AJ | October 1st, 2008 @ 06:10 AM

If the number of matching items is large (say > 500), then autocomplete performance degrades heavily.

  • Generating the list of candidates is extremely slow in IE6 and 7; though I suppose this is an IE performance bug, there might be implementation workarounds.

  • The mouseover code is extremely inefficient, and can cause the browsers to lag for seconds. The code is found in Autocompleter.Base.render(). On a mouseover, the code iterates through all the candidates in the list, setting or removing "selected" from their classnames. This is prohibitively slow as the list gets large. A solution is to replace the code:

for (var i = 0; i < this.entryCount; i++)
  this.index==i ?
     Element.addClassName(this.getEntry(i),"selected") :


if (this.selected_item)
this.selected_item = this.index+1;

(The +1 is to account for a 0 index; you can alternately use Prototype's isUndefined() function to determine if selected_item has been set.)

  • There are other minor improvements that could be made, such as not lowercase()ing the input string for each candidate in Autocompleter.Local.setOptions().


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script.aculo.us is an open-source JavaScript framework for visual effects and interface behaviours.
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