Merge pull request #7301 from giuseppe-straziota/performance-improvement

fix: Performance improvement for scattergl with many points. Issue #7065

Author: archmoj

draftlogs/7301_fix.md

@@ -0,0 +1,2 @@
+- Performance improvement for scattergl traces with many points [[#7301](https://github.com/plotly/plotly.js/pull/7301)],
+   with thanks to @giuseppe-straziota for the contribution!

src/components/fx/helpers.js

@@ -60,8 +60,13 @@ exports.getClosest = function(cd, distfn, pointData) {
         // this is the longest loop... if this bogs down, we may need
         // to create pre-sorted data (by x or y), not sure how to
         // do this for 'closest'
-        for(var i = 0; i < cd.length; i++) {
-            var newDistance = distfn(cd[i]);
+
+        // defined outside the for to improve the garbage collector performance
+        var newDistance = Infinity;
+        // the browser engine typically optimizes the length, but it is outside the cycle if it does not
+        var len = cd.length
+        for(var i = 0; i < len; i++) {
+            newDistance = distfn(cd[i]);
             if(newDistance <= pointData.distance) {
                 pointData.index = i;
                 pointData.distance = newDistance;