Sometime it is required to navigate user in webview on back press button rather than to exit webview so for this you can use the following code :

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if(event.getAction() == KeyEvent.ACTIONDOWN){
        switch(keyCode)
        {
            case KeyEvent.KEYCODEBACK:
                    if (mWebView.canGoBack()) {
                        mWebView.goBack();
                    } else {
                        cancel();
                    }

                return true;
        }

    }
    return super.onKeyDown(keyCode, event);
}

here you can set some properties on webview like this :

mWebView.getSettings().setJavaScriptEnabled(true);