Before talking about the need for defer parsing of JavaScript, it is essential for all to have a good understanding of JavaScript. This is because of many confusing JavaScript with Java. One must know that Java and JavaScript are not related in any way. Java is a programming language while the other is a scripting language. It finds its usage in input functions checking. For example, it checks that every information is given in a form before notification of it. This scripting language was developed by Netscape by Brendan Eich. Defer parsing of JavaScript is quintessential for increasing the speed of loading pages and also to improve the time taken for displaying any page while loading initially.
JavaScript finds its use in execution of functions which are otherwise difficult for CSSandHTML. These functions are necessary since they help to develop and form particular set of rules for buttons and other such features for a website. It happens like this; on clicking a contact form’s button for its submission, JavaScript will ensure that every input needed is there and if it is so, the user will get a confirmation for the success of it. This also leads to redirection for the next page or another form or the later part of the form. If the user hasn’t entered the details properly, he gets an error message that informs him of the missing part.
All these help to make a website more interactive and easy to access. Various things like contact forums, tweet buttons, Google+, subscription forms, etc. are developed with the help of this. However, JavaScript has its own share of glitches for which one needs to defer parsing of it. JavaScript prevents or blocks the rendering of a web page. This happens often and hampering web marketing approaches uses Search Engine Optimization tactics and hence the requirement of parsing. It has been faced by everyone that when JavaScript is placed on any document’s head, then all that is below the header will take time till the JavaScript is downloaded by the web browser. Many browsers have the capability of downloading 6 different scripts. In case of the older versions of the browsers the download limits goes down to 2. Now with this downloading capability, it becomes difficult for downloading the page.
Since most of the plugins add script to the document’s head, it becomes difficult to have it downloaded fast. Also there can be more than 8 or 10 plugins in a website for its different functions in the website. And every plugin requires a JavaScript, which therefore becomes difficult for the browser to load. There are generally two most used techniques for solving this. These are deferred loading of JavaScript and another used to <script sync> attribute wherever required at web designing time. These two prevents the blocking of the pages by JavaScript. The other processes are generally not used for they can be quite complicated and the mentioned techniques are quite easy to perform and gives fast results. With these you can have your problems solved and add necessary plugins to make your website more interactive.