Core: Refactor loops to avoid going behind array bounds#5839
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Current size diffs: |
mgol
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May 11, 2026
| // results (starting at index 1 because index 0 is always kept), then | ||
| // splice away the tail of duplicates. | ||
| for ( ; i < results.length; i++ ) { | ||
| for ( i = 1; i < results.length; i++ ) { |
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@gibson042 changes in this file resulted in the following size diffs compared to if I didn't touch the file:
last run
raw gz br Filename
+1 -7 +17 dist/jquery.min.js
+1 -6 -18 dist/jquery.slim.min.js
+1 -6 +35 dist-module/jquery.module.min.js
+1 -6 +31 dist-module/jquery.slim.module.min.js
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It's possible it'd go the other way round if we avoided initializers in loops and moved them to declarations, but it's not always possible, as sometimes the same variable is used in multiple loops.
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Reaching behind array bounds - which is what effectively happens if you check for `null`/`undefined` value instead of doing a `length` check - can trigger deopts in various JS engines. Switch to regular `length`-based loops. In the past, this was impractical as IE <9 used to clobber the `length` property if an element with the `name="length"` attribute was present, but this is no longer a concern.
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Summary
Reaching behind array bounds - which is what effectively happens if you check for
null/undefinedvalue instead of doing alengthcheck - can trigger deopts in various JS engines. Switch to regularlength-based loops.In the past, this was impractical as IE <9 used to clobber the
lengthproperty if an element with thename="length"attribute was present, but this is no longer a concern.Checklist
New tests have been added to show the fix or feature worksIf needed, a docs issue/PR was created at https://github.com/jquery/api.jquery.com