#script tag

When the browser’s HTML parser bumps into a <script> tag, normally, it will pause HTML parsing and wait for the <script> to both download and execute before resuming. 

This is usually why we would want to have <script> tags at the bottom of our html right before the closing </body> tag.

However, we can use async and defer to modify the behavior for better performance.

By using defer, we tell the HTML parser to continue parsing while the <script> downloads or loads. Then, when the parser is done at the end, the <script> will execute.

crossorigin is a thing too!

It’s not fully standardized yet, but there is a crossorigin attribute which is supported by some browsers. The general idea is that the browser doesn’t like to let you do much with resources loaded from a different ‘origin’ than the current page. (The origin is defined as the combination of the page’s protocol, hostname, and port. I.e. http://google.com:80).

This is to prevent you from, for example, making requests to your competitors website which cancels any accounts the current user might have (not nice!). Its connection to script tags is somewhat incidental though. The idea is if you apply a handler to the window.onerror event, that handler is provided with some information about the page and script which you perhaps shouldn’t have if you’re loading code from an external site. In secure browsers this info is not included unless you specify crossorigin.