Function getWaitFunction

test/e2e/test-controller-promise.js:255–294

* Simulate the WebDriver polling functionality to get the latest value * and mutate it with any `then` blocks that have been chained to the * ControllerPromise. * See ../../build-system/tasks/e2e/expect.js for real usage * @param {function(): function():(!Promise |T)}

(valueFunctionGetter)

     * @template T
     */
    function getWaitFunction(valueFunctionGetter) {
      return (conditionFn, opt_mutate) => {
        /**
         * Each call to `waitForValue` gets its own value function thunk.
         * This simulates the value returned by a WebDriver framework for
         * a request for a value e.g. from the DOM.
         * See {@link ../../build-system/tasks/e2e/selenium-webdriver-controller.js#getElementText}
         */
        const valueFunction = valueFunctionGetter();

        opt_mutate = opt_mutate || ((x) => x);
        return new Promise((resolve, reject) => {
          /**
           * Poll for the new value.
           * See {@link ../../build-system/tasks/e2e/selenium-webdriver-controller.js#getWaitFn_}
           */
          const id = setInterval(async () => {
            let value;
            try {
              value = await opt_mutate(await valueFunction());
            } catch (e) {
              clearInterval(id);
              reject(e);
              return;
            }

            /**
             * This resolves the promise that the Chai wrapper `expect.js` awaits.
             * The condition is passed in by the expectations and it
             * stops polling when the condition matches.
             * See {@link ../../build-system/tasks/e2e/expect.js#valueSatisfiesExpectation}
             */
            if (conditionFn(value)) {
              clearInterval(id);
              resolve(value);
            }
          }, 4);
        });
      };
    }
  });
});