.js

gainResult(fn) {
  return Promise.race([
    new Promise(resolve => {
      try {
        const ret = fn((err, result) => {
          if (err) {
            resolve({
              type: "async",
              error: err.message
            });
          } else {
            resolve({
              type: "async",
              value: result
            });
          }
        });
        if (ret instanceof Promise) {
          resolve(
            ret.then(
              res => ({
                type: "promise",
                value: res
              }),
              err => ({
                type: "promise",
                error: err.message
              })
            )
          );
        } else if (ret !== undefined) {
          resolve({
            type: "return",
            value: ret
          });
        }
      } catch (e) {
        resolve({
          error: e.message
        });
      }
    }),
    new Promise(resolve => {
      setTimeout(
        () =>
          resolve({
            type: "no result"
          }),
        1000
      );
    })
  ]);
}

From https://github.com/webpack/tapable/blob/master/lib/__tests__/HookTester.js