引用: https://www.runoob.com/js/js-function-definition.html
匿名函数自动调用表达式: (function(){})()
1 <p id="demo"></p> 2 3 <script> 4 (function(){document.getElementById("demo").innerHTML = "Hello World!";})() 5 </script>
Output: Hello World!
原文：https://www.cnblogs.com/goakon/p/9563459.html