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"use strict";
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const { readFile } = require("fs");
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const { promisify } = require("util");
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const readFileAsync = promisify(readFile);
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(async () => {
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  const data = await readFileAsync("hello.txt", "utf8");
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  debugger;
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  console.log(data);
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})();

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ᐅ node inspect index.js
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< Debugger listening on ws://127.0.0.1:9229/e1d19bde-2450-4d9b-9736-02fd
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35038351
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< For help, see: https://nodejs.org/en/docs/inspector
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< Debugger attached.
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Break on start in index.js:1
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> 1 (function (exports, require, module, __filename, __dirname) { 'use s
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trict';
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  2
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  3 const { readFile } = require('fs');
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debug>

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< Debugger listening on ws://127.0.0.1:9229/e1d19bde-2450-4d9b-9736-02fd
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35038351
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< For help, see: https://nodejs.org/en/docs/inspector
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< Debugger attached.
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Break on start in index.js:1
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> 1 (function (exports, require, module, __filename, __dirname) { 'use s
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trict';
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  2
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  3 const { readFile } = require('fs');
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debug> cont
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break in index.js:11
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  9   const data = await readFileAsync('hello.txt', 'utf8');
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 10
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>11   debugger;
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 12
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 13   console.log(data);
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debug>

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...
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 13   console.log(data);
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debug> repl
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Press Ctrl + C to leave debug repl
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> data
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'hello:)'
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> typeof readFileAsync
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'function'
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>

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  3 const { readFile } = require('fs');
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debug>
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debug> c
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break in index.js:11
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  9   const data = await readFileAsync('hello.txt', 'utf8');
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 10
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>11   debugger;
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 12
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 13   console.log(data);
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debug> c
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< hello:)
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< Waiting for the debugger to disconnect...
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debug>.exit

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ᐅ node --inspect-brk index.jsDebugger listening on ws://127.0.0.1:9229/b6e42f20-bbc5-4848-8c59-b25ccf
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e0a454
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For help, see: https://nodejs.org/en/docs/inspector

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"use strict";
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const http = require("http");
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http
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  .createServer((request, response) => {
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    debugger;
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    response.writeHead(200, { "Content-Type": "text/plain" });
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    response.write("hello:)");
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    response.end();
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  })
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  .listen(8080);

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ᐅ node --inspect server.js
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Debugger listening on ws://127.0.0.1:9229/61ea5e2c-6674-4a08-bd8a-f1cc1d8651bd
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For help, see: https://nodejs.org/en/docs/inspector
4
Debugger attached.

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< Debugger listening on ws://127.0.0.1:9229/e0e85f75-c4c9-4d53-ab45-cc83d69ad9ba< For help, see: https://nodejs.org/en/docs/inspector< Debugger attached.
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Break on start in index.js:1
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> 1 (function (exports, require, module, __filename, __dirname) { 'use strict';
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  2
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  3 const { readFile } = require('fs');
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debug> setBreakpoint(10)
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  6 const readFileAsync = promisify(readFile);
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  7
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  8 (async () => {
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  9   const data = await readFileAsync('hello.txt', 'utf8');
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 10
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>11   console.log(data);
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 12 })();
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 13
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debug> repl
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Press Ctrl + C to leave debug repl
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> data'hello:)'
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debug
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> c< hello:)
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< Waiting for the debugger to disconnect...
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debug> .exit

1
ᐅ node --prof index.js

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ᐅ node --prof-process isolate-0xNNNNNNNNN-v8.log > processed.txt

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 [JavaScript]:
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   ticks  total  nonlib   name
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      2    2.4%    2.5%  Builtin: KeyedStoreIC
4
      1    1.2%    1.3%  LazyCompile: ~NativeModule.require internal/bootstrap/loaders.js:138:34
5
      1    1.2%    1.3%  Builtin: CEntry_Return1_DontSaveFPRegs_ArgvOnStack_NoBuiltinExit
6

7
 [C++]:
8
   ticks  total  nonlib   name
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     22   26.8%   27.5%  T node::contextify::ContextifyScript::New(v8::FunctionCallbackInfo<v8::Value> const&)
10
      6    7.3%    7.5%  T v8::internal::Log::MessageBuilder& v8::internal::Log::MessageBuilder::operator<<<char const*>(char const*)
11
      3    3.7%    3.8%  t node::GetBinding(v8::FunctionCallbackInfo<v8::Value> const&)
12
      3    3.7%    3.8%  T node::TTYWrap::New(v8::FunctionCallbackInfo<v8::Value> const&)
13

14
 [Summary]:
15
   ticks  total  nonlib   name
16
      4    4.9%    5.0%  JavaScript
17
     74   90.2%   92.5%  C++
18
      4    4.9%    5.0%  GC
19
      2    2.4%          Shared libraries
20
      2    2.4%          Unaccounted

1
$ clinic flame -- node index.js

1
$ node --trace-gc test.js
2
[43929:0x102801c00]       39 ms: Scavenge 3.4 (6.3) -> 3.1 (7.3) MB, 0.9 / 0.0 ms  allocation failure
3
[43929:0x102801c00]       50 ms: Scavenge 3.6 (7.3) -> 3.5 (8.3) MB, 1.2 / 0.0 ms  allocation failure
4

5
$ node --optimize_for_size --max_old_space_size=4096 --gc_interval=100 #このようにV8のGCを操作することも可能

1
clinic doctor -- node server.js

1
const { performance, PerformanceObserver } = require("perf_hooks");
2
const React = require("react");
3
const { renderToString } = require("react-dom/server");
4

5
const render = performance.timerify(renderToString);
6
const obs = new PerformanceObserver((list, observer) => {
7
  const data = list.getEntries();
8

9
  data.forEach((l) => {
10
    if (l.name === "renderToString") console.log("duration", l.duration);
11
  });
12

13
  observer.disconnect();
14
});
15

16
obs.observe({ entryTypes: ["function"], buffered: true });
17

18
const Main = (props) => {
19
  return React.createElement(
20
    "ul",
21
    null,
22
    [...new Array(props.n)].map((_, i) => {
23
      return React.createElement("li", { key: i }, "test");
24
    }),
25
  );
26
};
27

28
render(Main(1000000));

1
$ node server.js
2
$ autocannon  localhost:8080 -c1000
3
Running 10s test @ http://localhost:8080
4
1000 connections
5

6
Stat         Avg     Stdev  Max
7
Latency (ms) 68.95   84.55  1594.74
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Req/Sec      14454.7 5049.5 21068
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Bytes/Sec    2.19 MB 769 kB 3.18 MB
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11
145k requests in 10s, 21.8 MB read
12
1 errors (0 timeouts)
13
autocannon localhost:8080 -c1000  4.91s user 2.37s system 69% cpu 10.433 total