bundle-wizard/src/functions/processTracing.js

Analyze the JavaScript loaded by a website

const tracium = require('tracium')

const longTaskThreshold = 150

const processTracing = async tracing => {
  let longTasks = []

  try {
    const tasks = tracium.computeMainThreadTasks(tracing, {
      flatten: true
    })

    longTasks = tasks
      .filter(t => t.kind === 'scriptEvaluation')
      .filter(t => t.duration > longTaskThreshold)

    //prevent circular json error
    longTasks.forEach(task => (task.children = []))
  } catch (e) {
    console.error('\nWarning: could not parse long task report, skipping')
  }

  const priorities = tracing.traceEvents
    .filter(event => event.args.data && event.args.data.priority)
    .map(event => event.args.data)
  return { priorities, longTasks }
}

module.exports = processTracing