[Q&A] 为什么把js脚本放到html页面的底部？

Images from different servers can be downloaded more than two at a time, but once your browser encounters a <script> tag, it can no longer download multiple items in parallel. Having them at the bottom means it will help speed up your page load time. 

一句话，提供页面加载速度，至于怎么提高，还是个很复杂的事情。