Optimization on mappers function in builtin.js (#186)

Optimize mappers function to load selective conversion rules for performance improvement

Signed-off-by: sayan404 <sayanmajumder0002@gmail.com>

bindings/node/builtin.js

@@ -1,26 +1,30 @@
-// mappers to store all the mappers of all drafts from draft3 to draft7
+// mappers to store all the mappers of required drafts in an array.
 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 indexMapper = new Map(drafts.map((draft, index) => [draft, index]))
+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)
+  return loadRequiredRules(fromIndex, toIndex)
 }
-
 exports.drafts = drafts