Mention the functionality which you can do with JavaScript

Given below are the things which you can do with JavaScript:

1. Give response to a user instantaneously – Suppose a user has just submitted a comment form on your website. It would be a nice idea to show a thank you message to the user instantaneously using JavaScript. The server can also do this but it might take a little while for your thank you message to appear to the user, depending on how busy the server is.
2. Make your web pages responsive to events – Since Web environments are dynamic, events happen all the time. With JavaScript, the web page can immediately react to these events the way you choose.
3. Detect visitors browser – JavaScript can be used to detect a visitor's browser. You can choose to load a page specifically tailored to that kind of browser, depending on the browser and its capabilities.
4. Creation of Cookies – JavaScript is quite efficient if you want to create cookies so that your visitors can enjoy a personalized experience the next time they visit your website.
5. Validation of Web Form data – JavaScript can be used to validate web-form data before the form is submitted to a server. This saves the server from extra processing.
6. There are tons of other functionality which can be implemented by JavaScript such as addition of cool animation effects to your web pages without using an external Flash plug-in, usage of the newest features of HTML5 such as canvas (to draw directly on your web page) and drag and drop capabilities, integrate your website with external web services such as Facebook, Twitter, etc.