Simple JavaScript client-side applications. Introducing Chrome Developer tools.
The DOM: Javascript manipulates the contents of the web page through a standard abstraction called the Document Object Model (DOM), hence the reason for this brief introduction.
jQuery: although not as popular as it once may have been, rumours of its death have likely been greatly exaggerated. Undoubtedly losing ground to modern frameworks. it will still probably be in widespread use for quite some time yet.
Use both native JavaScript and JQuery to access and manipulate the DOM.