util: improve util.inspect performance

* improve util.inspect performance
  This is a huge performance improvement in case of sparse arrays
  when using util.inspect as the hole will simple be skipped.

* use faster visibleKeys property lookup

* add inspect-array benchmark

PR-URL: https://github.com/nodejs/node/pull/14492
Fixes: https://github.com/nodejs/node/issues/14487
Reviewed-By: Alexey Orlenko <eaglexrlnk@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/benchmark/util/inspect-array.js b/benchmark/util/inspect-array.js
new file mode 100644
index 0000000000..44067b8b8f
--- /dev/null
+++ b/benchmark/util/inspect-array.js
@@ -0,0 +1,39 @@
+'use strict';
+
+const common = require('../common');
+const util = require('util');
+
+const bench = common.createBenchmark(main, {
+  n: [1e2],
+  len: [1e5],
+  type: [
+    'denseArray',
+    'sparseArray',
+    'mixedArray'
+  ]
+});
+
+function main(conf) {
+  const { n, len, type } = conf;
+  var arr = Array(len);
+  var i;
+
+  switch (type) {
+    case 'denseArray':
+      arr = arr.fill(0);
+      break;
+    case 'sparseArray':
+      break;
+    case 'mixedArray':
+      for (i = 0; i < n; i += 2)
+        arr[i] = i;
+      break;
+    default:
+      throw new Error(`Unsupported type ${type}`);
+  }
+  bench.start();
+  for (i = 0; i < n; i++) {
+    util.inspect(arr);
+  }
+  bench.end(n);
+}