JavaScript is a scripting language most often used for client-side web development. This means it runs on your visitor’s computer and so does not require constant downloads from your web site. One most important thing to remember is that Javascript and Java are not the same.They are two completely different computer languages. Its just that Javascript has the mention of Java in it. Almost all the web browsers have built in support for Javascript. This means your javascript code will run on the browser of your website visitor everytime he/she visits your page provided they have Javascript enabled on their respective browser.