benchmark: make the benchmark tool work with Node 10

Avoid using class fields in the benchmark tools since they are
not available in Node 10. This can be reverted when Node 10
reaches EOL.

PR-URL: #35817
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: Michael Dawson <midawson@redhat.com>
Reviewed-By: Mary Marchini <oss@mmarchini.me>

benchmark/common.js

@@ -4,24 +4,24 @@ const child_process = require('child_process');
 const http_benchmarkers = require('./_http-benchmarkers.js');
 
 class Benchmark {
-  // Used to make sure a benchmark only start a timer once
-  #started = false;
+  constructor(fn, configs, options = {}) {
+    // Used to make sure a benchmark only start a timer once
+    this._started = false;
 
-  // Indicate that the benchmark ended
-  #ended = false;
+    // Indicate that the benchmark ended
+    this._ended = false;
 
-  // Holds process.hrtime value
-  #time = [0, 0];
+    // Holds process.hrtime value
+    this._time = [0, 0];
 
-  // Use the file name as the name of the benchmark
-  name = require.main.filename.slice(__dirname.length + 1);
+    // Use the file name as the name of the benchmark
+    this.name = require.main.filename.slice(__dirname.length + 1);
 
-  // Execution arguments i.e. flags used to run the jobs
-  flags = process.env.NODE_BENCHMARK_FLAGS ?
-    process.env.NODE_BENCHMARK_FLAGS.split(/\s+/) :
-    [];
+    // Execution arguments i.e. flags used to run the jobs
+    this.flags = process.env.NODE_BENCHMARK_FLAGS ?
+      process.env.NODE_BENCHMARK_FLAGS.split(/\s+/) :
+      [];
 
-  constructor(fn, configs, options = {}) {
     // Parse job-specific configuration from the command line arguments
     const argv = process.argv.slice(2);
     const parsed_args = this._parseArgs(argv, configs, options);
@@ -214,21 +214,21 @@ class Benchmark {
   }
 
   start() {
-    if (this.#started) {
+    if (this._started) {
       throw new Error('Called start more than once in a single benchmark');
     }
-    this.#started = true;
-    this.#time = process.hrtime();
+    this._started = true;
+    this._time = process.hrtime();
   }
 
   end(operations) {
     // Get elapsed time now and do error checking later for accuracy.
-    const elapsed = process.hrtime(this.#time);
+    const elapsed = process.hrtime(this._time);
 
-    if (!this.#started) {
+    if (!this._started) {
       throw new Error('called end without start');
     }
-    if (this.#ended) {
+    if (this._ended) {
       throw new Error('called end multiple times');
     }
     if (typeof operations !== 'number') {
@@ -244,7 +244,7 @@ class Benchmark {
       elapsed[1] = 1;
     }
 
-    this.#ended = true;
+    this._ended = true;
     const time = elapsed[0] + elapsed[1] / 1e9;
     const rate = operations / time;
     this.report(rate, elapsed);