Promise wrapper, can be used in Node or in browser with transpiling

BusyPromise

export class BusyPromise {

  /**
   * Promise wrapper that calls pre and post methods. Can be used to auto increment and decrement a
   * counter, for example, or to indicate when busy and unbusy.
   * @param opts {Object}
   * @param [opts.pre] {Function} Function to execute before calling function
   * @param [opts.onResolve] {Function} Function to execute after function resolves
   * @param [opts.onReject] {Function} Function to execute if function rejects
   * @param fn {function} Same as function in new Promise(fn)
   */
  constructor (opts, fn) {
    this.opts = opts;
    this.opts.pre && this.opts.pre();
    this.p = new Promise((resolve, reject) => {
      fn((data) => {
        this.opts.onResolve && this.opts.onResolve();
        resolve(data);
      }, (err) => {
        this.opts.onReject && this.opts.onReject(err);
        reject(err);
      });
    });
  }

  then (onResolve, onReject) {
    return this.p.then(onResolve, onReject);
  }

  catch (onReject) {
    return this.p.catch(onReject);
  }
}

gistfile1.txt

export class DemoView {

  constructor() {
    this.busy = 0;
    this.busyOpts = {
      pre: () => {
        ++this.busy;
      },
      onResolve: () => {
        --this.busy;
      },
      onReject: (err) => {
        --this.busy;
        this.logger.error(err);
        this.alert.error(err);
      }
    };
  }

  waitWithBusyFlag() {
    return new BusyPromise(this.busyOpts, (resolve, reject) => {
      return this.wait().then(resolve, reject);
    });
  }
  
  wait() {
    return new Promise((resolve) => {
      setTimeout() => {
        resolve();
      }, 1000);
    });
  }
        
}