Speed up addLineStringEndpoints by 10x. #454

src/lib/browse/Filters.svelte

@@ -58,7 +58,7 @@
     filterTextCopy: string,
     filterAuthority: string,
     filterFundingProgramme: string,
-    filterCurrentMilestone: string,
+    filterCurrentMilestone: string
   ) {
     let filterNormalized = filterTextCopy.toLowerCase();
     let filterFeatures = (feature: FeatureUnion) => {
@@ -136,7 +136,12 @@
     $schemesGj = $schemesGj;
     counts = counts;
   }
-  $: filtersUpdated($filterText, filterAuthority, filterFundingProgramme, filterCurrentMilestone);
+  $: filtersUpdated(
+    $filterText,
+    filterAuthority,
+    filterFundingProgramme,
+    filterCurrentMilestone
+  );
 
   function metersToMiles(x: number): number {
     return x * 0.000621371;

src/lib/maplibre/utils.ts

@@ -186,24 +186,30 @@ export async function getStyleSpecification(
 }
 
 // Returns all the input features, additionally with a new point for every
-// LineString endpoint, with an endpoint=true property.
+// LineString endpoint, with an endpoint=true property. Note this drops any
+// foreign members on the input, and that it reuses object references of the
+// input for performance, rather than making a defensive deep copy.
 export function addLineStringEndpoints(
   input: FeatureCollection
 ): FeatureCollection {
-  let copy = JSON.parse(JSON.stringify(input));
+  let output: FeatureCollection = {
+    type: "FeatureCollection",
+    features: [],
+  };
   // Add points for the ends of every LineString
-  let endpoints = [];
-  for (let f of copy.features) {
-    if (f.geometry.type == "LineString" && !f.properties.hide_while_editing) {
+  for (let f of input.features) {
+    output.features.push(f);
+
+    if (f.geometry.type == "LineString" && !f.properties?.hide_while_editing) {
       for (let pt of [
         f.geometry.coordinates[0],
         f.geometry.coordinates[f.geometry.coordinates.length - 1],
       ]) {
-        endpoints.push({
+        output.features.push({
           type: "Feature",
           properties: {
             endpoint: true,
-            scheme_reference: f.properties.scheme_reference,
+            scheme_reference: f.properties?.scheme_reference,
           },
           geometry: {
             type: "Point",
@@ -213,8 +219,7 @@ export function addLineStringEndpoints(
       }
     }
   }
-  copy.features = copy.features.concat(endpoints);
-  return copy;
+  return output;
 }
 
 // Properties are guaranteed to exist