What is the use of JavaScriptExecutor in Selenium ?

JavaScriptExecutor is an interface which provides a mechanism to execute Javascript through the Selenium WebDriver. It provides "executescript" and "executeAsyncScript" methods, to run JavaScript in the context of the currently selected frame or window. An example of that is:

JavascriptExecutor js = (JavascriptExecutor) driver; 
js.executeScript(Script,Arguments);