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https://github.com/Polymer/pwa-helpers

Small helper methods or mixins to help you build web apps.
https://github.com/Polymer/pwa-helpers

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Small helper methods or mixins to help you build web apps.

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# pwa-helpers



[![Build Status](https://travis-ci.org/Polymer/pwa-helpers.svg?branch=master)](https://travis-ci.org/Polymer/pwa-helpers)

[![Published on npm](https://img.shields.io/npm/v/pwa-helpers.svg)](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

});

```