<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>js判断字符串是否有下划线</title>
<script src="https://code.jquery.com/jquery-3.1.1.min.js"></script>
</head>
<body>
<script>
var str="SH_20181030_1_25000";
var a=str.length;
var str1 = str.replace(/\_+/g,"")
var b=str1.length;
var c=a-b;
if(c!==3){
alert('名字下划线有问题');
}else{
alert("ok");
}
</script>
</body>
</html>