JavaScript Interface for Android Webview

Sanjeev

31 January 2024

In this article, we are going to learn how we can call android functions using javascript and vice versa using the javascript interface for android webview.

To know about webview and how it works, head over here.

For javascript to work in our webview, we need to enable it using webview settings.

Java:
webView.getSettings().setJavaScriptEnabled(true);

Kotlin:
webView.settings.javaScriptEnabled = true

Java:

webView.getSettings().setJavaScriptEnabled(true);

Kotlin:

webView.settings.javaScriptEnabled = true

Binding JavaScript to Android

Through an interface, WebView enables us to connect JavaScript code to Android code.

The class that provides the interface for JS must be passed, along with the name that will be used to show the instance in JS (for example, “Android”).

As a result, an interface called Android will be created for JavaScript that is running in WebView.

By using the interface we can achieve the following:

Run the methods described in Java/Kotlin from JS
Run the JS methods from Java/Kotlin

Calling Java/Kotlin Method from JavaScript

Create a JavaScript Interface Class

class MyJsInterface(private val mContext: Context) {
        @JavascriptInterface
        fun getAndroidVersion(): Int {
            return Build.VERSION.SDK_INT
        }

        @JavascriptInterface
        fun showToast() {
            Toast.makeText(mContext, "Toast from android", Toast.LENGTH_SHORT).show()
        }
    }

class MyJsInterface(private val mContext: Context) {

@JavascriptInterface

fun getAndroidVersion(): Int {

return Build.VERSION.SDK_INT

}

@JavascriptInterface

fun showToast() {

Toast.makeText(mContext, "Toast from android", Toast.LENGTH_SHORT).show()

}

Note: @JavascriptInterface annotation is required for API 17 and above.

Then install this interface using the following code.

Java:
webView.addJavascriptInterface(new MainActivity.MyJsInterface(this), "Android")

Kotlin:
webview.addJavascriptInterface(MyJsInterface(this), "Android")

Java:

webView.addJavascriptInterface(new MainActivity.MyJsInterface(this), "Android")

Kotlin:

webview.addJavascriptInterface(MyJsInterface(this), "Android")

Let’s create an HTML file where we will use our Java/Kotlin functions

Output:

Calling Java/Kotlin Method from JavaScript

Calling JS Function from Java/Kotlin

        findViewById&lt;Button&gt;(R.id.button).apply {
            setOnClickListener {
                // Calling JS function from Android
                // This name should match the name of the method that
                // you have declared in your JS file
                webView.loadUrl("javascript:increaseCount()")
            }
        }