As I told you earlier, when the parser finds this line, it goes to fetch the script and executes it. Then, after it’s done with this task, it goes on to parse the body.
This is bad because there is a lot of delay introduced. A very common solution to this issue is to put the script tag at the bottom of the page, just before the closing </body> tag.
In doing so, the script is loaded and executed after all the page is already parsed and loaded, which is a huge improvement over the head alternative.