为什么同一时间的Unix时间戳在不同的时区有所不同(why Unix Time Stamp for same time is different in different timezone)

 尽管脚本将被并行下载，但它们的执行顺序并不确定。 IE将按照它们完成下载的顺序执行它们，而Firefox则按照它们在DOM中附加的顺序执行它们。 
 
 这是个问题。 例如，说脚本A和脚本B是使用该技术添加的。 现在想象一下脚本A是jQuery，脚本B是这样做的： 
 
$(document).ready(function(){...})
 
 在IE中，如果出于任何原因（例如，网络流量，缓存未命中），脚本B在脚本A之前完成下载，因为它将在jQuery加载之前执行。 
 
 请参阅本文以获得更好的解释。 
 
 至于解决方案，您可以将<script>元素放置在页面尽可能远的地方 （例如，在关闭</body>元素之前）。尽管这不能保证并行下载，但它有助于缓解“阻塞”问题解决方案在寻址。 

Although scripts will be downloaded in parallel, the order in which they are executed is not deterministic. IE will execute them in the order they finish downloading in, whereas Firefox executes them in the order they are attached in the DOM.
 
This is a problem. For example, say script A and script B are added using that technique. Now imagine script A is jQuery, and script B does this:
 
$(document).ready(function(){...})
 
In IE you're screwed if for whatever reason (eg, network traffic, cache miss) script B finishes downloading before script A, because it will be executed before jQuery has been loaded.
 
See this article for a better explanation.
 
As for a solution, you can instead place the <script> elements as far down the page as possible (eg before the closing </body> element. Although this does not guarantee parallel downloads, it does help alleviate the "blocking" problem your solution is addressing.