Cache text encoding subarrays on-demand

lib/utils.js

@@ -469,16 +469,15 @@ if (typeof Buffer === 'function' && Buffer.prototype.utf8Slice) {
 const ENCODER = new TextEncoder();
 const encodeBuf = new Uint8Array(4096);
 const encodeBufs = [];
-// Believe it or not, `subarray` is actually quite expensive. To avoid the cost,
-// we call `subarray` once for each possible slice length and reuse those cached
-// views.
-for (let i = 0; i <= encodeBuf.length; i++) {
-  encodeBufs.push(encodeBuf.subarray(0, i));
-}
 
 function encodeSlice(str) {
   const {read, written} = ENCODER.encodeInto(str, encodeBuf);
   if (read === str.length) {
+    // Believe it or not, `subarray` is actually quite expensive. To avoid the
+    // cost, we cache and reuse `subarray`s.
+    if (!encodeBufs[written]) {
+      encodeBufs[written] = encodeBuf.subarray(0, written);
+    }
     return encodeBufs[written];
   }