wait-for.js

import waitUntil from '../wait-until';
import getElement from './-get-element';
import getElements from './-get-elements';
import toArray from './-to-array';
import { nextTickPromise } from '../-utils';

/**
  Used to wait for a particular selector to appear in the DOM. Due to the fact
  that it does not wait for general settledness, this is quite useful for testing
  interim DOM states (e.g. loading states, pending promises, etc).

  @param {string} selector the selector to wait for
  @param {Object} [options] the options to be used
  @param {number} [options.timeout=1000] the time to wait (in ms) for a match
  @param {number} [options.count=null] the number of elements that should match the provided selector (null means one or more)
  @returns {Element|Array<Element>} the element (or array of elements) that were being waited upon
*/
export default function waitFor(
  selector,
  { timeout = 1000, count = null, timeoutMessage = 'waitFor timed out' } = {}
) {
  return nextTickPromise().then(() => {
    if (!selector) {
      throw new Error('Must pass a selector to `waitFor`.');
    }

    let callback;
    if (count !== null) {
      callback = () => {
        let elements = getElements(selector);
        if (elements.length === count) {
          return toArray(elements);
        }
      };
    } else {
      callback = () => getElement(selector);
    }
    return waitUntil(callback, { timeout, timeoutMessage });
  });
}