1. 算术运算符
2. 赋值运算符
3. 用于字符串的+运算
如果把字符串与数字相加，结果将成为字符串
<!DOCTYPE html>
<html>
<head>
<title></title>
<meta charset="utf-8" />
</head>
<body>
<script>
//算术运算符
var y = 5;
var x1 = y + 2;
var x2 = y - 2;
var x3 = y * 2;
var x4 = y / 2;
var x5 = y % 2;
x6 = ++y;
x7 = --y;
document.write(x1 + " " + x2 + " " + x3 + " " + x4 + " " + x5 + " " + x6 + " " + x7+"</br>");
//赋值运算符
var a = 10, b = 5;
a = b;
document.write(a+" ");
a += b;
document.write(a + " ");
a -= b;
document.write(a + " ");
a *= b;
document.write(a + " ");
a /= b;
document.write(a + " ");
a %= b;
document.write(a + "</br>");
//用于字符串的+运算
//如果把字符串与数字相加，结果将成为字符串
x = 5 + 5;
document.write(x + "</br>");
x = "5" + "5";
document.write(x + "</br>");
x = 5 + "5";
document.write(x + "</br>");
</script>
</body>
</html>