react-native-render-html

An iOS/Android pure javascript react-native component that renders your HTML into 100% native views. It's made to be extremely customizable and easy to use and aims at being able to render anything you throw at it.

Based on the original work of Thomas Beverley, props to him.

react-native-render-html

Install

npm install react-native-render-html --save or yarn add react-native-render-html

Basic usage

import React, { Component } from 'react';
import { ScrollView, Dimensions } from 'react-native';
import HTML from 'react-native-render-html';

const htmlContent = `
    <h1>This HTML snippet is now rendered with native components !</h1>
    <h2>Enjoy a webview-free and blazing fast application</h2>
    <img src="https://i.imgur.com/dHLmxfO.jpg?2" />
    <em style="textAlign: center;">Look at how happy this native cat is</em>
`;

export default class Demo extends Component {
    render () {
        return (
            <ScrollView style={{ flex: 1 }}>
                <HTML html={htmlContent} imagesMaxWidth={Dimensions.get('window').width} />
            </ScrollView>
        );
    }
}

Props

Prop	Description	Type	Required/Default
`renderers`	Your custom renderers	`object`	Optional, some default ones are supplied (`<a>`, `<img>`...)
`html`	HTML string to parse and render	`string`	Required
`uri`	(experimental) remote website to parse and render	`string`	Optional
`decodeEntities`	Decode HTML entities of your content	`bool`	Optional, defaults to `true`
`imagesMaxWidth`	Resize your images to this maximum width, see images	`number`	Optional
`onLinkPress`	Fired with the event and the href as its arguments when tapping a link	`function`	Optional
`tagsStyles`	Provide your styles for specific HTML tags, see styling	`object`	Optional
`classesStyles`	Provide your styles for specific HTML classes, see styling	`object`	Optional
`containerStyle`	Custom style for the default container of the renderered HTML	`object`	Optional
`customWrapper`	Replace the default wrapper with a function that takes your content as the first parameter	`function`	Optional
`emSize`	The default value in pixels for `1em`	`number`	`14`
`baseFontSize`	The default fontSize applied to `<Text>` components	`number`	`14`
`alterData`	Target some specific texts and change their content, see altering content	`function`	Optional
`alterChildren`	Target some specific nested nodes and change them, see altering content	`function`	Optional
`ignoredTags`	HTML tags you don't want rendered, see ignoring HTML content	`array`	Optional, `['head', 'scripts']`
`ignoredStyles`	CSS styles from the `style` attribute you don't want rendered, see ignoring HTML content	`array`	Optional
`ignoreNodesFunction`	Return true in this custom function to ignore nodes very precisely, see ignoring HTML content	`function`	Optional

Demo

This component comes with a demo that showcases every feature presented here. It's very useful to keep track of bugs and rendering differences between the different versions of react-native.

It is mandatory to refer to an example of the demo or to provide one when submitting an issue or a pull request for a new feature.

Feel free to write more advanced examples and submit a pull-request for it, it will probably be very useful for other users.

Creating custom renderers

This is very useful if you want to make some very specific styling of your HTML content, or even implement custom HTML tags.

Just pass an object to the renderers prop with the tag name as the key, an a function as its value, like so :

renderers: {
    hr: () => <View style={{ width: '100%', height: 1, backgroundColor: 'blue' }} />
}

Here, we have overriden the default <br /> renderer and made it a blue line.

You can also create your own tags and use them in your HTML content :

const content = `<bluecircle></bluecircle>`;
...

renderers: {
    bluecircle: () => <View style={{ width: 20, height: 20, borderRadius: 10, backgroundColor: 'blue' }} />
}

Your renderers functions receive several arguments that will be very useful to make some very specific rendering.

htmlAttribs: attributes attached to the node, parsed in a react-native way
children : array with the children of the node
convertedCSSStyles : conversion of the style attribute from CSS to react-native's stylesheet
passProps : various useful information : groupInfo, parentTagName, parentIsText...

Styling

In addition to your custom renderers, you can apply specific styles to HTML tags (tagsStyles) or HTML classes (classesStyles). You can also combine these styles with your custom renderers.

Styling options override thesmelves, so you might render a custom HTML tag with a custom renderer like <bluecircle>, make it green with a class <bluecircle class="make-me-green"> or make it red by styling the tag itself.

The default style of your custom renderer will be merged to the one from your classesStyles which will also be merged by the style attribute.

Here's an usage example

// props
    tagsStyles: { i: { textAlign: 'center', fontStyle: 'italic', color: 'grey' } },
    classesStyles: { 'last-paragraph': { textAlign: 'right', color: 'teal', fontWeight: '800' } }

const html = `
    <i>Here, we have a style set on the "i" tag with the "tagsStyles" prop.</i>
    <p class="last-paragraph">Finally, this paragraph is style through the classesStyles prop</p>`;

Images

By default, unstyled images will be rendered with their respective height and width without resizing. You can force their dimensions by using the style attribute in your HTML content, or style them with a class or through the <img> tag.

If you can't set the dimension of each image in your content, you might find the imagesMaxWidth prop useful. It resizes (and keeps proportions) your images to a maximum width, ensuring that your images won't overflow out of your viewport.

A nice trick, demonstrated in the basic usage of this module is to use the Dimensions API of react-native : imagesMaxWidth={Dimensions.get('window').width}. You could substract a value to it to make a margin.

Please note that if you set width AND height through any mean of styling, imagesMaxWidth will be ignored.

Images with broken links will render an empty square with a thin border, similar to what safari renders in a webview.

Please note that all of these behaviours are implemented in the default <img> renderer. If you want to provide your own <img> renderer, you'll have to make this happen by yourself. You can use the img function in HTMLRenderers.js as a starting point.

Altering content

alterData and alterChildren props are very useful to make some modifications on the structure of your HTML before it's actually rendered with react components.

They both are functions that receive the parsed node as their first and only parameter. You must return your changes : a string with alterData and an array with alterChildren or a falsy value if you don't need to change anything.

alterData

alterData allows you to change the text content of your nodes. For instance, you can customize the content of <h1> and <h2> to render your titles in uppercase.

Here's how you would do that :

// ... your props
alterData: (node) => {
    let { parent, data } = node;
    if (parent && parent.name === 'h1') {
        // Texts elements are always children of wrappers, this is why we check the tag
        // with "parent.name" and not "name"
        return data.toUpperCase();
    } else {
        // Return a falsy value for anything else than the <h1> tag so nothing is altered
        return false;
    }
}

alterChildren

alterChildren allows you to change the children wrapped in any node. For instance, you might want to change the content of a a list.

Here's an example :

// ... your props
alterChildren: (node) => {
    const { children, name } = node;
    if (name === 'ol' && children && children.length) {
        // Keep only the first two elements of the list
        return children.splice(0, 2);
    } else {
        // Return a falsy value for anything else than the <ol> tag so nothing is altered
        return false;
    }
}

Ignoring HTML content

You can't expect native components to be able to render everything you can find in your browser. And you might not entirely trust your contributors, so here are 3 props allowing you to prevent disasters without sanitizing your HTML on the server-side (that doesn't mean you shouldn't !).

ignoredTags : array of ignored HTML tags, by default head and scripts are removed
ignoredStyles : array of ignored CSS rules. Nothing is ignored by default
ignoreNodesFunction : this is a cumbersome, yet powerful, way of ignoring very specific stuff.

Please note that if you supply ignoredTags, you will override the default ignored ones. There are a lot of them, if you want to keep them and add you own, you can do something like :

import { IGNORED_TAGS } from 'react-native-render-html/HTMLUtils';
...

// your props
ignoredTags={[ ...IGNORED_TAGS, 'tag1', 'tag2']}

ignoreNodesFunction receives 3 parameters : node, parentTagName and parentIsText.

node is the result of the HTML parsing, which allows you to look for children, check the parent's markup and much more. parentTagName is a conveniant way to access the parent of your node, and parentIsText is a great way to make sure you won't be rendering a <View> inside a <Text> which, right now, makes react-native crash.

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