<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<script>
//仅声明了函数,不会自执行,报错
function aa(){
console.log('aa');
}()
//自执行情况 </script>
<script>
//自执行情况
//小括号
(function(){
console.log('a1');
})(); //赋值操作
var a = function(){
console.log('a2');
}(); //逻辑运算符
!function(){
console.log('a3');
}(); //数学运算符
+function(){
console.log('a4');
}();
</script>
</body>
</html>
注意所写的代码是声明还是执行..