How to run javascript in Flutter WebView

Have you ever consider how to run or execute Javascript code in flutter webview?  Imagine using a flutter webview in your application and you want a situation where an alert dialog can be triggered understand certain condition.

Here we will look at a simple code example on how to run javascript code in flutter webview

We are not going to use the official flutter webview widget rather we are going to use the flutter webview community edition. This is a webview project begin undertaken by flutter community and it is not the official flutter webview.

You can read more about third party webview plugin here (FlutterWebviewPlugin).

To make running javascript code simple, the FlutterWebviewPlugin class has a method name evalJavascript(). This method is use to evaluate any javascript code and execute it.

1. Add flutter_webview plugin in pubspec.yaml

name: flutter_app
description: A new Flutter application.

# The following defines the version and build number for your application.
# A version number is three numbers separated by dots, like 1.2.43
# followed by an optional build number separated by a +.
# Both the version and the builder number may be overridden in flutter
# build by specifying --build-name and --build-number, respectively.
# Read more about versioning at semver.org.
version: 1.0.0+1

environment:
  sdk: ">=2.0.0-dev.68.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter

  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^0.1.2
  http: 0.12.0
  ##sqflite: 0.13.0+1
  path_provider: 0.4.1
  ##zoomable_image: 1.2.1+1
  ##multi_image_picker: 2.3.32
  dio: 2.0.22
  shared_preferences: 0.4.3
  flare_flutter: any
  flutter_webview_plugin: 0.3.0+2
  webview_flutter: 0.2.0


dev_dependencies:
  flutter_test:
    sdk: flutter


# For information on the generic Dart part of this file, see the
# following page: https://www.dartlang.org/tools/pub/pubspec

# The following section is specific to Flutter.
flutter:

  # The following line ensures that the Material Icons font is
  # included with your application, so that you can use the icons in
  # the material Icons class.
  uses-material-design: true

  assets:
    - assets/html_code.html
    - assets/iframe.html
    - assets/js_lib.html


  # To add assets to your application, add an assets section, like this:
  # assets:
  #  - images/a_dot_burr.jpeg
  #  - images/a_dot_ham.jpeg

  # An image asset can refer to one or more resolution-specific "variants", see
  # https://flutter.io/assets-and-images/#resolution-aware.

  # For details regarding adding assets from package dependencies, see
  # https://flutter.io/assets-and-images/#from-packages

  # To add custom fonts to your application, add a fonts section here,
  # in this "flutter" section. Each entry in this list should have a
  # "family" key with the font family name, and a "fonts" key with a
  # list giving the asset and other descriptors for the font. For
  # example:
  # For details regarding fonts from package dependencies,
  # see https://flutter.io/custom-fonts/#from-packages

2. Create main.dart if it does not already exist

This is the entry point of our application. Open the file and add the code below.

import 'package:flutter/material.dart';
import 'run_javascript.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: RunJSInWebView(),
    );
  }
}

In the above code, the new dart class we will create later is assigned to the home property of the MaterialAppwidget. Lets create run_javascript.dart file.

3. Create run_javascript.dart in lib folder

Create a new dart file in the lib directory. I will name mine run_javascript.dart. You can use a filename of your choice.

Open the file and add the code below.

import 'package:flutter/material.dart';
import 'package:flutter_webview_plugin/flutter_webview_plugin.dart';

class RunJSInWebView extends StatefulWidget {
  @override
  RunJSInWebViewState createState() {
    return new RunJSInWebViewState();
  }
}

class RunJSInWebViewState extends State<RunJSInWebView> {
  final flutterWebviewPlugin = new FlutterWebviewPlugin();

  @override
  void initState(){
    super.initState();
    flutterWebviewPlugin.evalJavascript("alert('Inducesmile.com')");
    
    
  }
  @override
  void dispose() {
    flutterWebviewPlugin.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return WebviewScaffold(
      url: 'https://inducesmile.com',
      hidden: true,
      appBar: AppBar(title: Text("Run JS in Webview")),
    );
  }
}

4. Run your app

You can use flutter command to run your app – $ flutter run

If everything goes well, you will see a website similar to the image below in your flutter webview.

If you have any question or suggestions kindly use the comment box or you can contact us directly through our contact page below.

 

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