Why scripts at the end of body tag

Solution 1:

Scripts, historically, blocked additional resources from being downloaded more quickly. By placing them at the bottom, your style, content, and media could download more quickly giving the perception of improved performance.

Further reading: The async and defer attributes.

Solution 2:

In my opinion, this is an outdated practice. More recently, the preference is for JavaScript to separate any code that requires the DOM to be present into a "DOMContentLoaded" event listener. This isn't necessarily all logic; lots of code can initialize without access to the complete DOM.

It's true that this causes a small moment when only the script file is being retrieved, and nothing else (for instance, images). This small window can be skipped by adding the async attribute, but even without it I recommend putting script tags in the head so that the browser knows as soon as possible to load them, rather than saving them (and any future JS-initiated requests) for last.

Solution 3:

It is a best practice to put JavaScript tags just before the closing tag rather than in the section of your HTML.

The reason for this is that HTML loads from top to bottom. The head loads first, then the body, and then everything inside the body. If we put our JavaScript links in the head section, the entire JavaScript file will load before loading any of the HTML, which could cause a few problems.

1.If you have code in your JavaScript that alters HTML as soon as the JavaScript file loads, there won't actually be any HTML elements available for it to affect yet, so it will seem as though the JavaScript code isn't working, and you may get errors. 2.If you have a lot of JavaScript, it can visibly slow the loading of your page because it loads all of the JavaScript before it loads any of the HTML. When you place your JavaScript links at the bottom of your HTML body, it gives the HTML time to load before any of the JavaScript loads, which can prevent errors, and speed up website response time.

One more thing: While it is best to include your Javascript at the end of your HTML , putting your Javascript in the of your HTML doesn't ALWAYS cause errors. When using jQuery, it is common to put all of your code inside a "document ready" function:

$("document").ready(function(){ // your code here });

This function basically says, don't run any of the code inside until the document is ready, or fully loaded. This will prevent any errors, but it can still slow down the loading time of your HTML, which is why it is still best to include the script after all of the HTML.