striplog.js

/*
Post-processing to allow deoptigate to work with browser collected traces.

To collect a trace from a Chromium-based browser, run with flags such as the below:

  %browser_exe% --no-sandbox --disable-extensions --js-flags="--trace-ic --nologfile-per-isolate --logfile=/temp/trace/v8.log" C:\temp\trace\default.html

Rename the generated `v8.log` to `v8.pre.log`, to preserve the orignal log
before processing with the below (that specific filename is expected).

Then run this script in the same directory as `v8.pre.log` to process the
log file into something deoptigate can handle (see comments for details).
This will create a new `v8.log` file.

  node striplog.js

Then run deoptigate to open the log file, e,g, `npx deoptigate`
*/

const fs = require('fs');

let log_text = fs.readFileSync("v8.pre.log", "utf8");
let log_lines = log_text.split('\n');

const badLines = /(extensions::SafeBuiltins:)|(v8\/LoadTimes:)/;
// Web servers will have a prefix like: http://localhost:8000/app.js (needs to be just app.js)
// Files from Windows something like: file:///C:/temp/app.js (needs to be just /temp/app.js)
// Files from Linux something like: file:///home/bill/app.js (needs to be just /home/bill/app.js)
const webPrefix = /((https?:\/\/[^\/]*\/)|(file:\/\/\/[a-zA-Z]:)|(file:\/\/))/;

let new_lines = "";
log_lines.forEach( line => {
  // Removes lines containing "extensions::SafeBuiltins:" or "v8/LoadTimes:"
  if (badLines.test(line)) return;
  // Remove the http://localhost:8000/-like prefix.
  const scrubbed_line = line.replace(webPrefix, "");
  new_lines += scrubbed_line + "\n";
});

fs.writeFileSync("v8.log", new_lines);