Cache with Map.

Author: sandinmyjoints

lib/parsers/string.js

@@ -1,21 +1,30 @@
 'use strict';
 
 const Iconv = require('iconv-lite');
+const decoderCache = new Map();
 
-exports.decode = function(buffer, encoding, start, end, options) {
+exports.decode = function (buffer, encoding, start, end, options) {
   if (Buffer.isEncoding(encoding)) {
     return buffer.toString(encoding, start, end);
   }
 
-  const decoder = Iconv.getDecoder(encoding, options || {});
+  const decoderArgs = { encoding, options: options || {} };
+  const decoder =
+    decoderCache.get(decoderArgs) ||
+    decoderCache
+      .set(
+        decoderArgs,
+        Iconv.getDecoder(decoderArgs.encoding, decoderArgs.options),
+      )
+      .get(decoderArgs);
 
   const res = decoder.write(buffer.slice(start, end));
   const trail = decoder.end();
 
   return trail ? res + trail : res;
 };
 
-exports.encode = function(string, encoding, options) {
+exports.encode = function (string, encoding, options) {
   if (Buffer.isEncoding(encoding)) {
     return Buffer.from(string, encoding);
   }