Optimization on mappers function in builtin.js

bindings/node/builtin.js

@@ -1,26 +1,29 @@
-// mappers to store all the mappers of all drafts from draft3 to draft7
 const drafts = ['draft3', 'draft4', 'draft6', 'draft7', '2019-09', '2020-12']
-const mappers = drafts.flatMap((draft, index) => {
-  const rules = [require(`../../rules/jsonschema-${draft}-to-${draft}.json`)]
-  if (index + 1 < drafts.length) {
-    rules.push(require(`../../rules/jsonschema-${draft}-to-${drafts[index + 1]}.json`))
-  }
-  return rules
-})
-
 // indexMapper maps drafts to their index in the mappers array. This is used to find the subarray of mappers to be returned.
 const indexMapper = new Map(drafts.map((draft, index) => [draft, index * 2]))
-
+const loadRequiredRules = (fromIndex, toIndex) => {
+  const mappers = [];
+  for (let index = fromIndex; index <= toIndex; index++) {
+    const draft = drafts[index];
+    const rule = require(`../../rules/jsonschema-${draft}-to-${draft}.json`);
+    mappers.push(rule);
+    if (index < toIndex) {
+      const nextDraft = drafts[index + 1];
+      const nextRule = require(`../../rules/jsonschema-${draft}-to-${nextDraft}.json`);
+      mappers.push(nextRule);
+    }
+  }
+  return mappers;
+};
 exports.builtin = (from, to) => {
   if (!indexMapper.has(from)) {
     throw new Error(`Invalid "from": ${from}`)
-  } else if (!indexMapper.has(to)) {
+  }
+  if (!indexMapper.has(to)) {
     throw new Error(`Invalid "to": ${to}`)
   }
-
   const fromIndex = indexMapper.get(from)
   const toIndex = indexMapper.get(to)
-  return mappers.slice(fromIndex, toIndex + 1)
-}
-
-exports.drafts = drafts
+  return loadRequiredRules(fromIndex, toIndex);
+};
+exports.drafts = drafts