1.浏览器对script引用的js文件分两步，下载，下载完毕后马上执行；这两步都会阻塞浏览器继续解析。
2.加入defer属性，<script defer type="text/javascript" src="some.js" ></script>，浏览器会异步加载js，待DOMContentLoaded后顺序执行js。
3.预加载js，自定义执行时机。
<script language="javascript" type="text/javascript"> function cachejs(script_filename){ var cache = document.createElement(\'object\'); cache.data = script_filename; cache.id = "coolshell_script_cache_id"; cache.width = 0; cache.height = 0; document.body.appendChild(cache); } function loadjs(script_filename) { var script = document.createElement(\'script\'); script.setAttribute(\'type\', \'text/javascript\'); script.setAttribute(\'src\', script_filename); script.setAttribute(\'id\', \'coolshell_script_id\'); script_id = document.getElementById(\'coolshell_script_id\'); if(script_id){ document.getElementsByTagName(\'head\')[0].removeChild(script_id); } document.getElementsByTagName(\'head\')[0].appendChild(script); } function LoadJS(){ var script = \'./alert.js\'; loadjs(script); } </script> ... <p style="cursor: pointer" onclick="LoadJS()">Click to load alert.js </p> ... ... <script> cachejs(\'./alert.js\'); </script>