axios/lib/helpers/callbackify.js

import utils from "../utils.js";

const callbackify = (fn, reducer) => {
  return utils.isAsyncFn(fn) ? function (...args) {
    const cb = args.pop();
    fn.apply(this, args).then((value) => {
      try {
        reducer ? cb(null, ...reducer(value)) : cb(null, value);
      } catch (err) {
        cb(err);
      }
    }, cb);
  } : fn;
}

export default callbackify;