This document walks you through the most common use cases for React Native WebView. It doesn't cover [the full API](Reference.md), but after reading it and looking at the sample code snippets you should have a good sense for how the WebView works and common patterns for using the WebView.
The simplest way to use the WebView is to simply pipe in the HTML you want to display. Note that setting an `html` source requires the [originWhiteList](Reference.md#originWhiteList) property to be set to `['*']`.
```js
import React, { Component } from 'react';
import { WebView } from 'react-native-webview';
class MyInlineWeb extends Component {
render() {
return (
<WebView
originWhitelist={['*']}
source={{ html: '<h1>This is a static HTML source!</h1>' }}
/>
);
}
}
```
Passing a new static html source will cause the WebView to rerender.
Sometimes you would have bundled an HTML file along with the app and would like to load the HTML asset into your WebView. To do this on iOS, you can just import the html file like any other asset as shown below.
However on Android, you need to place the HTML file inside your android project's asset directory. For example, if `local-site.html` is your HTML file and you'd like to load it into the webview, you should move the file to your project's android asset directory which is `your-project/android/app/src/main/assets/`. Then you can load the html file as shown in the following code block
Sometimes you want to intercept a user tapping on a link in your webview and do something different than navigating there in the webview. Here's some example code on how you might do that using the `onNavigationStateChange` function.
##### Check for File Upload support, with `static isFileUploadSupported()`
File Upload using `<input type="file" />` is not supported for Android 4.4 KitKat (see [details](https://github.com/delight-im/Android-AdvancedWebView/issues/4#issuecomment-70372146)):
You can control **single** or **multiple** file selection by specifing the [`multiple`](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/file#multiple) attribute on your `input` element:
This runs the JavaScript in the `runFirst` string once the page is loaded. In this case, you can see that both the body style was changed to red and the alert showed up after 2 seconds.
<imgalt="screenshot of Github repo"width="200"src="https://user-images.githubusercontent.com/1479215/53609254-e5dc9c00-3b7a-11e9-9118-bc4e520ce6ca.png"/>
#### The `injectedJavaScriptBeforeContentLoaded` prop
This is a script that runs **before** the web page loads for the first time. It only runs once, even if the page is reloaded or navigated away. This is useful if you want to inject anything into the window, localstorage, or document prior to the web code executing.
```jsx
import React, { Component } from 'react';
import { View } from 'react-native';
import { WebView } from 'react-native-webview';
export default class App extends Component {
render() {
const runFirst = `
window.isNativeApp = true;
true; // note: this is required, or you'll sometimes get silent failures
This runs the JavaScript in the `runFirst` string before the page is loaded. In this case, the value of `window.isNativeApp` will be set to true before the web code executes.
While convenient, the downside to the previously mentioned `injectedJavaScript` prop is that it only runs once. That's why we also expose a method on the webview ref called `injectJavaScript` (note the slightly different name!).
Being able to send JavaScript to the web page is great, but what about when the web page wants to communicate back to your React Native code? This is where `window.ReactNativeWebView.postMessage` and the `onMessage` prop come in.
<imgalt="Alert showing communication from web page to React Native"width="200"src="https://user-images.githubusercontent.com/1479215/53671269-7e822300-3c32-11e9-9937-7ddc34ba8af3.png"/>
### Working with custom headers, sessions, and cookies
#### Setting Custom Headers
In React Native WebView, you can set a custom header like this:
```jsx
<WebView
source={{
uri: 'http://example.com',
headers: {
'my-custom-header-key': 'my-custom-header-value',
},
}}
/>
```
This will set the header on the first load, but not on subsequent page navigations.
In order to work around this, you can track the current URL, intercept new page loads, and navigate to them yourself ([original credit for this technique to Chirag Shah from Big Binary](https://blog.bigbinary.com/2016/07/26/passing-request-headers-on-each-webview-request-in-react-native.html)):
When you do, you'll likely want to enable the [sharedCookiesEnabled](Reference#sharedCookiesEnabled) prop as well.
```jsx
const App = () => {
return (
<WebView
source={{ uri: 'http://example.com' }}
sharedCookiesEnabled={true}
/>
);
};
```
If you'd like to send custom cookies in the WebView itself, you can do so in a custom header, like this:
```jsx
const App = () => {
return (
<WebView
source={{
uri: 'http://example.com',
headers: {
Cookie: 'cookie1=asdf; cookie2=dfasdfdas',
},
}}
sharedCookiesEnabled={true}
/>
);
};
```
Note that these cookies will only be sent on the first request unless you use the technique above for [setting custom headers on each page load](#Setting-Custom-Headers).
