Run JavaScript in Android apps (library)

Evaluates JavaScript and gets results. This is an alternative to evaluateJavascript method of the WebView. Supports Android version 3.0 (Honeycomb) and newer.

Get JAR file

Download jsevaluator.jar. You can also build it yourself with Eclipse. It will be built into JSEvaluator/bin/jsevaluator.jar.

Setup

To add JSEvaluator to your app in Eclipse:

1. File > Import JSEvaluator project.
2. Open properties for your app project.
3. Select Libraries tab in Java Build Path.
4. Click Add JARs... button and select jsevaluator.jar.
5. In your project properties click Order and export tab.
6. Tick jsevaluator.jar.

Usage

Create evaluator instance:

JsEvaluator jsEvaluator = new JsEvaluator(this);

this is a reference to your activity.

Evaluate JavaScript

jsEvaluator.evaluate("2 * 17", new JsCallback() {
  @Override
  public void onResult(final String result) {
    // get result here (optional)
  }
});

Call a JavaScript function

jsEvaluator.callFunction("function myFunction(a, b, c, a) { return 'result'; }",
  new JsCallback() {

  @Override
  public void onResult(final String result) {
    // get result here
  }
}, "myFunction", "parameter 1", "parameter 2", 912, 101.3);

Any number of string, int or double parameters can be supplied.

How it works

Behind the scenes it creates a WebView and feeds it JavaScript code for evaluation:

mWebView = new WebView(context);
String javascript = "<script>myObj.returnResult('Hello World')</script>";
String base64 = Base64.encodeToString(data, Base64.DEFAULT);
mWebView.loadUrl("data:text/html;charset=utf-8;base64," + base64);

The result of evaluation is sent back into Android activity:

public class JavaScriptInterface {
	public void returnResult(String result) {
		// result from JavaScript
	}
}

mWebView.addJavascriptInterface(new JavaScriptInterface(), "myObj");

Tests

Tests are located in JsEvaluatorTests project.

Run as Android Application for manual testing.

Or run as Android JUnit Test for unit testing.

Android versions tested:

• 3.0 (Honeycomb)
• 4.0.3 (Ice Cream Sandwich)
• 4.1.2 (Jelly Bean)
• 4.2.2 (Jelly Bean)
• 4.3 (Jelly Bean)
• 4.4.2 (KitKat)
• 5.0 (Lollipop)

Result is returned asynchronously

The result from JavaScript is returned asynchronously in the UI thread. It is recommended to evaluate in the UI thread as well.

// somewhere in UI thread ...
jsEvaluator.evaluate("2 * 17", new JsCallback() {
  @Override
  public void onResult(final String result) {
    // Result is returned here asynchronously in UI thread
  }
});

JavaScript is evaluated in new context

Each time the JavaScript is evaluated in the new context. It can not access the result of a previous evaluation. Please concatenate all your JavaScript to one string and evaluate it in one go.

For example, if you need to load jQuery libary and then use it:

String jQuery = "/*! jQuery JavaScript Library v2.1.1 ...";
jsEvaluator.evaluate(jQuery + "; $.isNumeric(123)", new JsCallback() { ...

Feedback

If you have any issues or need help please do not hesitate to create an issue ticket.