A web worker wrapper for loading scripts from strings, and executing functions as promises

usage.js

(async () => {
  const worker = new WorkerScript();
  await worker.loadScript(`
    return new Promise((resolve) => {
      setTimeout(() => {
        resolve('Sample output for ' + inputs.hello);
      }, 500)
    })
  `);
  const output = await worker.run({ hello: 'world'});
  console.log('output', output);
});

web-worker.js

class WorkerScript {
  constructor() {
    this.requestId = 0;
    const wrapper = `
      let fn = undefined;
      self.addEventListener('message', async ({ data }) => {
        const { type, payload, id } = data;
        const response = {
          id,
          payload: undefined,
          error: false,
        };
        try {
          switch (type) {
            case 'load-script': {
              fn = new Function('inputs', payload);
              break;
            }
            case 'run': {
              response.payload = await fn(payload);
              break;
            }
          }
        } catch (ex) {
          response.error = true;
          response.payload = ex.toString();
        }
        self.postMessage(response);
      });
    `;

    const blob = new Blob([wrapper], {type: 'application/javascript'});
    this.worker = new Worker(URL.createObjectURL(blob));
  }

  async evaluate(type, payload) {
    return await new Promise((resolve, reject) => {
      const currentId = this.requestId++
      const handler = ({ data }) => {
        const { id, payload, error } = data;
        if (id === currentId) {
          if (error) {
            reject(error);
          } else {
            resolve(payload);
          }
          this.worker.removeEventListener('message', handler);
        }
      };
      this.worker.addEventListener('message', handler);
      this.worker.postMessage({
        type,
        payload,
        id: currentId,
      });
    })
  }

  async loadScript(script) {
    return await this.evaluate('load-script', script);
  }

  async run(data) {
    return await this.evaluate('run', data);
  }
}