When web page is loaded, Chromium engine creates JavaScript Context instance. This instance represents context in which all JavaScript code is executed. The JavaScript Context instance is created when web page is loaded completely, but JavaScript code on it hasn't been executed yet. To get notifications about JavaScript Context creation use the ScriptContextListener.onScriptContextCreated(ScriptContextEvent event) event.

When web page is unloaded because of loading another web page or reloading existing one, Chromium engine destroys JavaScript Context and disposes all JavaScript objects running in scope of this context. To get notifications about JavaScript Context disposal use the ScriptContextListener.onScriptContextDestroyed(ScriptContextEvent event) event.

You might want to execute some JavaScript code before any other JavaScript on the loaded web page is executed. For example, to inject your own JavaScript objects/functions/properties. JxBrowser API provides functionality that allows receiving notifications before JavaScript code is executed on the loaded web page. To get such notification you must register ScriptContextListener and override its onScriptContextCreated(ScriptContextEvent event) method. Inside this method you can execute your JavaScript code. It will be executed before any other JavaScript on the loaded web page is executed. For example:

browser.addScriptContextListener(new ScriptContextAdapter() {
    public void onScriptContextCreated(ScriptContextEvent event) {
        Browser browser = event.getBrowser();
        // Access and modify document.title property before any other
        // JavaScript on the loaded web page has been executed.
        JSValue document = browser.executeJavaScriptAndReturnValue("document");
        document.asObject().setProperty("title", "My title");