完成注册功能

1. js文件： onclick函数return True时才提交表单，return False时不提交表单。
2. html文件：
   1. <form>中设置 action和method="post"
   2. <input> 中设置 name
3. 主py文件中：
   1. from flask import  request, redirect, url_for
   2. @app.route('/regist/', methods=['GET', 'POST’])

def regist():

   if request.method == 'GET':

        return render_template('regist.html')

   else:

        username = request.form.get(‘username’)#获取form中的数据

        判断用户名是否存在

        存到数据库中

        redirect重定向到登录页

function fnLogin() {
    var oUname = document.getElementById("uname")
    var oUpass = document.getElementById("upass")
     var oUpass2=document.getElementById("upass2");
    var oError = document.getElementById("error_box")
    var isErrer = true;

    oError.innerHTML="<br>"
    if (oUname.value.length > 20 || oUname.value.length < 6) {
        oError.innerHTML = "请输入用户名6-20位字符"
        isErrer = false
        return isErrer;
    }else if ((oUname.value.charCodeAt(0)>=48)&&(oUname.value.charCodeAt(0)<=57)){
        oError.innerHTML="用户名首字母必须是字母"
        isErrer = false
        return isErrer;
    }else for(var i=0; i<oUname.value.length;i++){
        if((oUname.value.charCodeAt(i)<48)||(oUname.value.charCodeAt(i)>57)&&(oUname.value.charCodeAt(i)<97)||(oUname.value.charCodeAt(i)>122)){
            oError.innerHTML="用户名必须为字母或数字";
            isErrer = false
            return isErrer;
        }

    }




    if (oUpass.value.length > 20 || oUpass.value.length < 6) {
        oError.innerHTML = "请输入密码 6-20位字符"

        isErrer = false
        return isErrer;
    }
     else if (oUpass.value!==oUpass2.value){
        oError.innerHTML="两次密码不一致";
        isErrer = false
        return isErrer;
    }

        return true;
//        window.alert("注册成功")

@app.route('/register/',methods=['GET','POST'])
def register():
    if request.method == 'GET':
         return render_template('register.html')
    else:
        username = request.form.get('username')
        password = request.form.get('password')
        nickname = request.form.get('nickname')
        user = User.query.filter( User.username == username).first()
        if user:
            return'username existed'
        else:
            user = User(username=username,password=password,nickname=nickname)
            db.session.add(user)
            db.session.commit()
            return redirect(url_for('login'))