Run some Javascript in Flutter Webview

Question

How can I run Javascript in flutter_webview_plugin? I tried with this:

onPressed: () {
   flutterWebviewPlugin.evalJavascript('<script language="JavaScript" type="text/javascript">alert("Hello World")</script>');
},

But nothing happens.

I thought with flutterWebviewPlugin.evalJavascript it's possible to run Javascript in a Webview. Did I do something wrong?

Answer 1

flutterWebviewPlugin.evalJavascript('<script language="JavaScript" type="text/javascript">alert("Hello World")</script>')

expects JavaScript, not HTML

<script language="JavaScript" type="text/javascript">alert("Hello World")</script>

is HTML.

Try

flutterWebviewPlugin.evalJavascript('alert("Hello World")')

Answer 2

You can try my plugin flutter_inappwebview, which is a Flutter plugin that allows you to add inline WebViews or open an in-app browser window and has a lot of events, methods, and options to control WebViews.

To run some js, you can use:

• Future<dynamic> evaluateJavascript({@required String source}): Evaluates JavaScript code into the WebView and returns the result of the evaluation.
• Future<void> injectJavascriptFileFromUrl({@required String urlFile}): Injects an external JavaScript file into the WebView from a defined url.
• Future<void> injectJavascriptFileFromAsset({@required String assetFilePath}): Injects a JavaScript file into the WebView from the flutter assets directory (see more here on how to load a file from the assets folder).

Full example:

import 'dart:async';

import 'package:flutter/material.dart';

import 'package:flutter_inappwebview/flutter_inappwebview.dart';

Future main() async {
  runApp(new MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => new _MyAppState();
}

class _MyAppState extends State<MyApp> {

  @override
  void initState() {
    super.initState();
  }

  @override
  void dispose() {
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        home: InAppWebViewPage()
    );
  }
}

class InAppWebViewPage extends StatefulWidget {
  @override
  _InAppWebViewPageState createState() => new _InAppWebViewPageState();
}

class _InAppWebViewPageState extends State<InAppWebViewPage> {
  InAppWebViewController webView;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
            title: Text("InAppWebView")
        ),
        body: Container(
            child: Column(children: <Widget>[
              Expanded(
                child: Container(
                  child: InAppWebView(
                    initialUrl: "https://www.example.org/",
                    initialHeaders: {},
                    initialOptions: InAppWebViewWidgetOptions(
                      inAppWebViewOptions: InAppWebViewOptions(
                        debuggingEnabled: true,
                      ),
                    ),
                    onWebViewCreated: (InAppWebViewController controller) {
                      webView = controller;
                    },
                    onLoadStart: (InAppWebViewController controller, String url) {

                    },
                    onLoadStop: (InAppWebViewController controller, String url) async {
                      int result1 = await controller.evaluateJavascript(source: "10 + 20;");
                      print(result1); // 30

                      String result2 = await controller.evaluateJavascript(source: """
                        var firstname = "Foo";
                        var lastname = "Bar";
                        firstname + " " + lastname;
                      """);
                      print(result2); // Foo Bar

                      // inject javascript file from an url
                      await controller.injectJavascriptFileFromUrl(urlFile: "https://code.jquery.com/jquery-3.3.1.min.js");
                      // wait for jquery to be loaded
                      await Future.delayed(Duration(milliseconds: 1000));
                      String result3 = await controller.evaluateJavascript(source: "\$('body').html();");
                      print(result3); // prints the body html

                      // inject javascript file from assets folder
                      await controller.injectJavascriptFileFromAsset(assetFilePath: "assets/myJavascriptFile.js");
                    },
                  ),
                ),
              ),
            ]))
    );
  }
}

Answer 3

Well, nothing happened because flutter webview does not support javascript alert function. Try writing a javascript function that changes the value of the innerText of an HTML element and then call the function using .evalJavascript to see the result.

Answer 4

This is how your Webview widget should look like

WebView(
    initialUrl: 'http://<domain>',
    javascriptMode: JavascriptMode.unrestricted,
    onWebViewCreated: (WebViewController webViewController) {
      webViewController.evaluateJavascript(
          'alert('hello from flutter)');
    }

Make use of webViewController anywhere in your code

Answer 5

I have debug with iOS part of flutter_webview_plugin.

For iOS part

Found it's related to iOS native part iOS WKWebView not showing javascript alert() dialog .

Good example of implement code are at gist.

I have create a fix for this.

Temp solution

You can use

flutter_webview_plugin:
    git:
      ref: "dev/fix_alert_not_work_in_webview"
      url: "https://github.com/jerryzhoujw/flutter_webview_plugin"
      source: git

this as temp in pubspec.yaml before merge PR.