use array methods findIndex() and at()

lib/layer/themes/graduated.mjs

@@ -12,31 +12,16 @@ export default function(theme, feature) {
 
   if (!isNaN(catValue) && catValue !== null) {
 
-    let catStyle;
-
-    // Iterate through cat array.
-    for (let i = 0; i < theme.cat_arr.length; i++) {
-
-      theme.cat_arr[i].style ??= theme.cat_arr[i]  
-
-      // Break iteration is cat value is below current cat array value.
-      if (catValue <= parseFloat(theme.cat_arr[i].value)){
-
-        //Set a style if one has not been set yet
-        if(!catStyle){
-          catStyle ??= structuredClone(theme.cat_arr[i].style)
-          delete catStyle.label
-        }
-        break;
-      } 
-
-      //Set the style for the element
-      catStyle = structuredClone(theme.cat_arr[i].style)
-      delete catStyle.label
-
-    }
-
-    // Merge catStyle for vector features.
+    const isLassThan = cat => catValue <= cat.value;
+
+    let index = theme.cat_arr.findIndex(isLassThan)
+
+    let cat = theme.cat_arr.at(index)
+
+    let catStyle = structuredClone(cat.style || cat)
+
+    delete catStyle.label
+
     mapp.utils.merge(feature.style, catStyle)
   }
 }