cache buffer in local var

lib/util/createHash.js

@@ -67,25 +67,26 @@ class BulkUpdateDecorator extends Hash {
 	 */
 	digest(encoding) {
 		let digestCache;
+		const buffer = this.buffer;
 		if (this.hash === undefined) {
 			// short data for hash, we can use caching
 			const cacheKey = `${this.hashKey}-${encoding}`;
 			digestCache = digestCaches[cacheKey];
 			if (digestCache === undefined) {
 				digestCache = digestCaches[cacheKey] = new Map();
 			}
-			const cacheEntry = digestCache.get(this.buffer);
+			const cacheEntry = digestCache.get(buffer);
 			if (cacheEntry !== undefined) return cacheEntry;
 			this.hash = this.hashFactory();
 		}
-		if (this.buffer.length > 0) {
-			this.hash.update(this.buffer);
+		if (buffer.length > 0) {
+			this.hash.update(buffer);
 		}
 		const digestResult = this.hash.digest(encoding);
 		const result =
 			typeof digestResult === "string" ? digestResult : digestResult.toString();
 		if (digestCache !== undefined) {
-			digestCache.set(this.buffer, result);
+			digestCache.set(buffer, result);
 		}
 		return result;
 	}