# React Native WebView Guide

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.

_This guide is currently a work in progress._

## Guide Index

- [Basic Inline HTML](Guide.md#basic-inline-html)
- [Basic URL Source](Guide.md#basic-url-source)
- [Loading local HTML files](Guide.md#loading-local-html-files)
- [Controlling navigation state changes](Guide.md#controlling-navigation-state-changes)
- [Add support for File Upload](Guide.md#add-support-for-file-upload)
- [Multiple files upload](Guide.md#multiple-files-upload)
- [Add support for File Download](Guide.md#add-support-for-file-download)
- [Communicating between JS and Native](Guide.md#communicating-between-js-and-native)
- [Working with custom headers, sessions, and cookies](Guide.md#working-with-custom-headers-sessions-and-cookies)

### Basic inline HTML

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.

### Basic URL Source

This is the most common use-case for WebView.

```js
import React, { Component } from 'react';
import { WebView } from 'react-native-webview';

class MyWeb extends Component {
  render() {
    return (
      <WebView source={{ uri: 'https://facebook.github.io/react-native/' }} />
    );
  }
}
```

### Loading local HTML files

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.

```js
import React, { Component } from 'react';
import { WebView } from 'react-native-webview';

const myHtmlFile = require("./my-asset-folder/local-site.html");

class MyWeb extends Component {
  render() {
    return (
      <WebView source={myHtmlFile} />
    );
  }
}
```

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/src/main/assets/`. Then you can load the html file as shown in the following code block

```js
import React, { Component } from 'react';
import { WebView } from 'react-native-webview';

class MyWeb extends Component {
  render() {
    return (
      <WebView source={{ uri: "file:///android_asset/local-site.html" }} />
    );
  }
}
```

### Controlling navigation state changes

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.

```js
import React, { Component } from 'react';
import { WebView } from 'react-native-webview';

class MyWeb extends Component {
  webview = null;

  render() {
    return (
      <WebView
        ref={ref => (this.webview = ref)}
        source={{ uri: 'https://facebook.github.io/react-native/' }}
        onNavigationStateChange={this.handleWebViewNavigationStateChange}
      />
    );
  }

  handleWebViewNavigationStateChange = newNavState => {
    // newNavState looks something like this:
    // {
    //   url?: string;
    //   title?: string;
    //   loading?: boolean;
    //   canGoBack?: boolean;
    //   canGoForward?: boolean;
    // }
    const { url } = newNavState;
    if (!url) return;

    // handle certain doctypes
    if (url.includes('.pdf')) {
      this.webview.stopLoading();
      // open a modal with the PDF viewer
    }

    // one way to handle a successful form submit is via query strings
    if (url.includes('?message=success')) {
      this.webview.stopLoading();
      // maybe close this view?
    }

    // one way to handle errors is via query string
    if (url.includes('?errors=true')) {
      this.webview.stopLoading();
    }

    // redirect somewhere else
    if (url.includes('google.com')) {
      const newURL = 'https://facebook.github.io/react-native/';
      const redirectTo = 'window.location = "' + newURL + '"';
      this.webview.injectJavaScript(redirectTo);
    }
  };
}
```

### Add support for File Upload

##### iOS

For iOS, all you need to do is specify the permissions in your `ios/[project]/Info.plist` file:

Photo capture:

```
<key>NSCameraUsageDescription</key>
<string>Take pictures for certain activities</string>
```

Gallery selection:

```
<key>NSPhotoLibraryUsageDescription</key>
<string>Select pictures for certain activities</string>
```

Video recording:

```
<key>NSMicrophoneUsageDescription</key>
<string>Need microphone access for recording videos</string>
```

##### Android

Add permission in AndroidManifest.xml:

```xml
<manifest ...>
  ......

  <!-- this is required only for Android 4.1-5.1 (api 16-22)  -->
  <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

  ......
</manifest>
```

##### 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)):

```
import { WebView } from "react-native-webview";

WebView.isFileUploadSupported().then(res => {
  if (res === true) {
    // file upload is supported
  } else {
    // not file upload support
  }
});

```

### Multiple Files Upload

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:

```
// multiple file selection
<input type="file" multiple />

// single file selection
<input type="file" />
```

### Add support for File Download

##### iOS

For iOS, all you need to do is specify the permissions in your `ios/[project]/Info.plist` file:

Save to gallery:

```
<key>NSPhotoLibraryAddUsageDescription</key>
<string>Save pictures for certain activities.</string>
```

##### Android

Add permission in AndroidManifest.xml:

```xml
<manifest ...>
  ......

  <!-- this is required to save files on Android  -->
  <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

  ......
</manifest>
```

### Communicating between JS and Native

You will often find yourself wanting to send messages to the web pages loaded by your webviews and also receiving messages back from those web pages.

To accomplish this, React Native WebView exposes three different options:

1. React Native -> Web: The `injectedJavaScript` prop
2. React Native -> Web: The `injectJavaScript` method
3. Web -> React Native: The `postMessage` method and `onMessage` prop

#### The `injectedJavaScript` prop

This is a script that runs immediately after the web page loads for the first time. It only runs once, even if the page is reloaded or navigated away.

```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 = `
      document.body.style.backgroundColor = 'red';
      setTimeout(function() { window.alert('hi') }, 2000);
      true; // note: this is required, or you'll sometimes get silent failures
    `;
    return (
      <View style={{ flex: 1 }}>
        <WebView
          source={{
            uri:
              'https://github.com/react-native-community/react-native-webview',
          }}
          injectedJavaScript={runFirst}
        />
      </View>
    );
  }
}
```

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.

<img alt="screenshot of Github repo" width="200" src="https://user-images.githubusercontent.com/1479215/53609254-e5dc9c00-3b7a-11e9-9118-bc4e520ce6ca.png" />

_Under the hood_

> On iOS, `injectedJavaScript` runs a method on WebView called `evaluateJavaScript:completionHandler:`
> On Android, `injectedJavaScript` runs a method on the Android WebView called `evaluateJavascriptWithFallback`


#### 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
    `;
    return (
      <View style={{ flex: 1 }}>
        <WebView
          source={{
            uri:
              'https://github.com/react-native-community/react-native-webview',
          }}
          injectedJavaScriptBeforeContentLoaded={runFirst}
        />
      </View>
    );
  }
}
```

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. 

#### The `injectJavaScript` method

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!).

```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 run = `
      document.body.style.backgroundColor = 'blue';
      true;
    `;

    setTimeout(() => {
      this.webref.injectJavaScript(run);
    }, 3000);

    return (
      <View style={{ flex: 1 }}>
        <WebView
          ref={r => (this.webref = r)}
          source={{
            uri:
              'https://github.com/react-native-community/react-native-webview',
          }}
        />
      </View>
    );
  }
}
```

After 3 seconds, this code turns the background blue:

<img alt="Screenshot of app showing injected javascript" width="200" src="https://user-images.githubusercontent.com/1479215/53670433-93a98280-3c2f-11e9-85a5-0e4650993817.png" />

_Under the hood_

> On iOS, `injectJavaScript` calls WebView's `evaluateJS:andThen:`
> On Android, `injectJavaScript` calls Android WebView's `evaluateJavascriptWithFallback` method

#### The `window.ReactNativeWebView.postMessage` method and `onMessage` prop

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.

You _must_ set `onMessage` or the `window.ReactNativeWebView.postMessage` method will not be injected into the web page.

`window.ReactNativeWebView.postMessage` only accepts one argument which must be a string.

```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 html = `
      <html>
      <head></head>
      <body>
        <script>
          setTimeout(function () {
            window.ReactNativeWebView.postMessage("Hello!")
          }, 2000)
        </script>
      </body>
      </html>
    `;

    return (
      <View style={{ flex: 1 }}>
        <WebView
          source={{ html }}
          onMessage={event => {
            alert(event.nativeEvent.data);
          }}
        />
      </View>
    );
  }
}
```

This code will result in this alert:

<img alt="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)):

```jsx
const CustomHeaderWebView = props => {
  const { uri, onLoadStart, ...restProps } = props;
  const [currentURI, setURI] = useState(props.source.uri);
  const newSource = { ...props.source, uri: currentURI };

  return (
    <WebView
      {...restProps}
      source={newSource}
      onShouldStartLoadWithRequest={request => {
        // If we're loading the current URI, allow it to load
        if (request.url === currentURI) return true;
        // We're loading a new URL -- change state first
        setURI(request.url);
        return false;
      }}
    />
  );
};

<CustomHeaderWebView
  source={{
    uri: 'http://example.com',
    headers: {
      'my-custom-header-key': 'my-custom-header-value',
    },
  }}
/>;
```

#### Managing Cookies

You can set cookies on the React Native side using the [react-native-cookies](https://github.com/joeferraro/react-native-cookies) package.

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).