code-event-handler

This is a JavaScript interface to v8::CodeEventHandler.

Install

npm install code-event-handler

Usage

const CodeEventHandler = require('code-event-handler')

const events = new CodeEventHandler(event => {
  console.log(event)
})

events.enable()

setTimeout(() => {
  events.disable()
}, 1000)

API

I've simply described the API surface area with TypeScript interfaces for now. More in-depth docs will come later.

enum CodeEventType {
  Builtin = 'Builtin',
  Callback = 'Callback',
  Eval = 'Eval',
  Function = 'Function',
  InterpretedFunction = 'InterpretedFunction',
  Handler = 'Handler',
  BytecodeHandler = 'BytecodeHandler',
  LazyCompile = 'LazyCompile',
  RegExp = 'RegExp',
  Script = 'Script',
  Stub = 'Stub',
  Relocation = 'Relocation'
}

interface CodeEvent {
  address: string;
  previousAddress: string;
  size: number;
  functionName: string;
  scriptName: string;
  line: number;
  column: number;
  type: CodeEventType;
  comment: string;
}

interface CodeEventHandler {
  new (handler: (event: CodeEvent): void);
  enable(): void;
  disable(): void;
}

Perf map files

An additional helper to use this interface to generate perf map files exists in perf-map.js. You can preload it into your app by doing:

node -r code-event-handler/perf-map.js app.js

It also accepts environment varialbes for PERF_MAP_PATH to change the path from the default /tmp/perf-$pid.map and PERF_MAP_TYPES which should be a comma-separated list of type names to record.