There is a way to 'force' the injection of your local Javascript files from local assets (e.g., assets/js/script.js), and to circumvent the 'Not allowed to load local resource : file:///android_assets/js/script.js ...' issue.

It is similar to what described in another thread (Android webview, loading javascript file in assets folder), with additional BASE64 encoding/decoding for representing your Javascript file as a printable string.

I am using an Android 4.4.2, API level 19 Virtual Device.

Here are some code snippets:

[assets/js/script.js]:

    'use strict';



    function test() {

       // ... do something

    }



    // more Javascript

[MainActivity.java]:

    ...



    WebView myWebView = (WebView) findViewById(R.id.webView);

    WebSettings webSettings = myWebView.getSettings();



    webSettings.setJavaScriptEnabled(true);

    webSettings.setAllowUniversalAccessFromFileURLs(true);

    myWebView.setWebViewClient(new WebViewClient() {

       @Override

       public boolean shouldOverrideUrlLoading(WebView view, String url) {

          return false;

       }



       @Override

       public void onPageFinished(WebView view, String url) {

          super.onPageFinished(view, url);



          injectScriptFile(view, js/script.js); // see below ...



          // test if the script was loaded

          view.loadUrl(javascript:setTimeout(test(), 500));

       }



       private void injectScriptFile(WebView view, String scriptFile) {

          InputStream input;

          try {

             input = getAssets().open(scriptFile);

             byte[] buffer = new byte[input.available()];

             input.read(buffer);

             input.close();



             // String-ify the script byte-array using BASE64 encoding !!!

             String encoded = Base64.encodeToString(buffer, Base64.NO_WRAP);

             view.loadUrl(javascript:(function() { +

                          var parent = document.getElementsByTagName('head').item(0); +

                          var script = document.createElement('script'); +

                          script.type = 'text/javascript'; +

             // Tell the browser to BASE64-decode the string into your script !!!

                          script.innerHTML = window.atob(' + encoded + '); +

                          parent.appendChild(script) +

                          })());

          } catch (IOException e) {

             // TODO Auto-generated catch block

             e.printStackTrace();

          }

       }

    });



    myWebView.loadUrl(http://www.example.com);



    ...