Small helper methods or mixins to help you build web apps.
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keanulee Merge pull request #47 from abdonrd/patch-1
Fix Twitter metadata fields
Latest commit 5cb02ba Nov 12, 2018


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Small helper methods or mixins to help build a PWA, and reduce the boilerplate you might have to write. There are many different ways in which you could write these helpers; use these if you want a simple starting point.

Basic helpers

These are vanilla JavaScript methods that can be used regardless of which frameworks or libraries your application is written in.


Basic router that calls a callback whenever the location is updated.


import { installRouter } from 'pwa-helpers/router.js';

installRouter((location) => handleNavigation(location));

For example, if you're using this router in a Redux-connected component, you could dispatch an action in the callback:

import { installRouter } from 'pwa-helpers/router.js';
import { navigate } from '../actions/app.js';

installRouter((location) => store.dispatch(navigate(location)));

If you need to force a navigation to a new location programmatically, you can do so by pushing a new state using the History API, and then manually calling the callback with the new location:

window.history.pushState({}, '', '/new-route');

Optionally, you can use the second argument to read the event that caused the navigation. For example, you may want to scroll to top only after a link click.

installRouter((location, event) => {
  // Only scroll to top on link clicks, not popstate events.
  if (event && event.type === 'click') {
    window.scrollTo(0, 0);


Utility method that calls a callback whenever the network connectivity of the app changes. The callback should take a boolean parameter (with true meaning the network is offline, and false meaning online)


import { installOfflineWatcher } from 'pwa-helpers/network.js';

installOfflineWatcher((offline) => {
  console.log('You are ' + offline ? ' offline' : 'online');


Utility method that updates the page's open graph and Twitter card metadata. It takes an object as a parameter with the following properties: title | description | url | image.

If the url is not specified, window.location.href will be used; for all other properties, if they aren't specified, then that metadata field will not be set.

Example (in your top level element or document, or in the router callback):

import { updateMetadata } from 'pwa-helpers/metadata.js';

  title: 'My App - view 1',
  description: 'This is my sample app',
  url: window.location.href,
  image: '/assets/view1-hero.png'


Utility method that calls a callback whenever a media-query matches in response to the viewport size changing. The callback should take a boolean parameter (with true meaning the media query is matched).


import { installMediaQueryWatcher } from 'pwa-helpers/media-query.js';

installMediaQueryWatcher(`(min-width: 600px)`, (matches) => {
  console.log(matches ? 'wide screen' : 'narrow sreen');

Test helpers

Utility methods to be used inside of testing frameworks, to reduce some testing boilerplate.


This is an axe-core reporter that returns an Error containing every a11y violation for an element. Use this if you want to include axe-core in automated Mocha tests, etc.

Example (in a Mocha test):

import 'axe-core/axe.min.js';
import { axeReport } from 'pwa-helpers/axe-report.js';

describe('button', function() {
  it('is accessible', function() {
    const button = document.createElement('button');
    button.textContent = 'click this';  // Test should fail without this line.
    return axeReport(button);

Redux helpers

These utility methods are useful if your application is using Redux for state management.


This is a JavaScript mixin that you can use to connect a Custom Element base class to a Redux store. The stateChanged(state) method will be called when the state is updated.


import { connect } from 'pwa-helpers/connect-mixin.js';

class MyElement extends connect(store)(HTMLElement) {
  stateChanged(state) {
    this.textContent =;


A Redux store enhancer that lets you lazy-install reducers after the store has booted up. Use this if your application lazy-loads routes that are connected to a Redux store.


import { combineReducers } from 'redux';
import { lazyReducerEnhancer } from 'pwa-helpers/lazy-reducer-enhancer.js';
import someReducer from './reducers/someReducer.js';

export const store = createStore(
  (state, action) => state,

Then, in your page/element, you can lazy load a specific reducer with: