Handling retries client-side for Google Apps Script add-ons

google.script.run.withRetry.js

// Handle retries when calling Apps Script functions,
// from the client-side (i.e. a browser).
//
// @usage:
//  - google.script.run.withRetry().myFunction() // Will retry "myFunction" 2 times
//  - google.script.run.withRetry(5).myFunction() // Will retry "myFunction" 5 times
//
// /!\ Known caveats. The method withUserObject(object) is not supported.

if (google && google.script && google.script.run) {
  google.script.run.withRetry = function (maxRetries) {
    return new (function () {
      this._successHandler = null;
      this._failureHandler = null;

      this.withSuccessHandler = function (callback) {
        this._successHandler = callback;
        return this;
      };

      this.withFailureHandler = function (callback) {
        this._failureHandler = callback;
        return this;
      };

      function _runWithRetry(backendFunction, nRetries, successHandler, failureHandler, _arguments) {
        let _run = google.script.run;
        let _totalRetries = isNaN(nRetries) ? 0 : nRetries;
        let _maxRetries = typeof maxRetries === "number" ? maxRetries : 2;

        if (!_run[backendFunction]) {
          throw new Error(backendFunction + " is not defined");
        }

        if (successHandler) {
          _run = _run.withSuccessHandler(successHandler);
        }

        _run = _run.withFailureHandler(function (err) {
          if (_totalRetries < _maxRetries) {
            return _runWithRetry(backendFunction, _totalRetries + 1, successHandler, failureHandler, _arguments);
          }

          if (failureHandler) {
            return failureHandler(err);
          }
        });

        const _maximumBackoff = 32 * 1000;
        const _randomMilliseconds = Math.round(Math.random() * 1000);
        const _backoffTime = Math.min(Math.pow(2, _totalRetries - 2) * 1000 + _randomMilliseconds, _maximumBackoff);
        const _executionDelay = _totalRetries > 0 ? _backoffTime : 0;

        window.setTimeout(function () {
          _run[backendFunction].apply(null, _arguments);
        }, _executionDelay);
      }

      this._run = function () {
        _runWithRetry(this._backendFunction, 0, this._successHandler, this._failureHandler, arguments);
      };

      const _backendFunctions = [];

      for (let key in google.script.run) {
        if (key.indexOf("with") === 0) {
          continue;
        }

        _backendFunctions.push(key);
      }

      for (let i = 0; i < _backendFunctions.length; i++) {
        const functionName = _backendFunctions[i];

        this[functionName] = new Function(
          'this._backendFunction = "' + functionName + '"; this._run.apply(this, arguments)'
        );
      }
    })();
  };
}