pwa-helpers
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Small helper methods or mixins to help you build web apps.
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# pwa-helpers
[](https://travis-ci.org/Polymer/pwa-helpers)
[](https://www.npmjs.com/package/pwa-helpers)
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.
### `router.js`
Basic router that calls a callback whenever the location is updated.
Example:
```js
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:
```js
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:
```js
window.history.pushState({}, '', '/new-route');
handleNavigation(window.location);
```
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.
```js
installRouter((location, event) => {
// Only scroll to top on link clicks, not popstate events.
if (event && event.type === 'click') {
window.scrollTo(0, 0);
}
handleNavigation(location);
});
```
### `network.js`
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)
Example:
```js
import { installOfflineWatcher } from 'pwa-helpers/network.js';
installOfflineWatcher((offline) => {
console.log('You are ' + offline ? ' offline' : 'online');
});
```
### `metadata.js`
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):
```js
import { updateMetadata } from 'pwa-helpers/metadata.js';
updateMetadata({
title: 'My App - view 1',
description: 'This is my sample app',
url: window.location.href,
image: '/assets/view1-hero.png'
});
```
### `media-query.js`
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).
Example:
```js
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.
### `axe-report.js`
This is an [axe-core](https://github.com/dequelabs/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):
```js
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.
### `connect-mixin.js`
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.
Example:
```js
import { connect } from 'pwa-helpers/connect-mixin.js';
class MyElement extends connect(store)(HTMLElement) {
stateChanged(state) {
this.textContent = state.data.count.toString();
}
}
```
### `lazy-reducer-enhancer.js`
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.
Example:
```js
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,
compose(lazyReducerEnhancer(combineReducers))
);
```
Then, in your page/element, you can lazy load a specific reducer with:
```js
store.addReducers({
someReducer
});
```