node-custom-tracing-hacks.js

// HACK: Use Node's testing APIs to be able to log custom trace
//       events. I… genuinely didn't find a better way to do
//       local nodejs custom tracing??
//
// To enable tracing, run this with:
//     node --expose-internals --trace-event-categories app
//
// Without that, the require will throw an error, so the trace
// functions will be no-ops!
let trace;
let withTrace;
try {
  const { internalBinding } = require("internal/test/binding");
  const rawTrace = internalBinding("trace_events").trace;

  // `trace` lets you wrap an async block with start/end trace events!
  // Like: `await trace("fetchThatOneWebpage", {url}, () => fetch(url))`
  let nextTraceId = 0;
  trace = async (eventName, traceArgs, fn) => {
    let traceId = nextTraceId++;
    rawTrace("b".charCodeAt(0), "app", eventName, traceId, traceArgs);
    try {
      return await fn();
    } finally {
      rawTrace("e".charCodeAt(0), "app", eventName, traceId, traceArgs);
    }
  };

  // `withTrace` lets you wrap an async function with start/end trace
  // events for every time you call it! First parameter is the function,
  // second parameter is a function to transform the arguments into an
  // object of safe, serializable arguments to log with the trace.
  withTrace =
    (fn, getTraceArgsFromFnArgs, name = null) =>
    (...args) =>
      trace(name || fn.name, getTraceArgsFromFnArgs(...args), () =>
        fn(...args)
      );
} catch (e) {
  trace = (_, __, fn) => fn();
  withTrace = (fn) => fn;
}