Inline web worker

app.js

const worker = new InlineWorker((data) => {
  postMessage(data.a + data.b)
})

worker.start({ a: 1, b: 2 }, (result) => {
  console.log(result) // output: 3
})

worker.start({ a: 1, b: 2 })
  .then((result) => console.log(result))
  .catch((err) => console.error(err))

InlineWorker.js

class WebWorker {
  constructor (code) {
    code = `onmessage = (e) => (${code.toString()})(e.data)`
    this.blob = window.URL.createObjectURL(new window.Blob([code], { type: 'application/javascript' }))
  }

  start (initialData, callback) {
    if (typeof callback === 'function') {
      this.worker = new window.Worker(this.blob)
      this.worker.onmessage = (e) => callback(e.data)
      this.worker.postMessage(initialData)
    } else {
      return new Promise((resolve, reject) => {
        try {
          this.worker = new window.Worker(this.blob)
          this.worker.onmessage = (e) => resolve(e.data)
          this.worker.postMessage(initialData)
        } catch (ex) {
          reject(ex)
        }
      })
    }
  }

  terminate () {
    this.worker.terminate()
  }
}