var username = document.getElementById('username'), password = document.getElementById('password'), password2 = document.getElementById('password-2'), exp1 = /[A-Za-z]{1}[A-Za-z0-9]{4,11}/, exp2 = /[A-Za-z0-9]{3,15}/; if(!(exp1.test(username.value))){ alert('用户名以字母开头，长度为5-16个字符!'); return false; }else if(!(exp2.test(password.value))){ alert('密码由三到15位数字字母组成!'); return false; }else if(password.value !== password2.value ){ alert('两次密码必须相同!'); return false; }