检查用户是不是已存在于 localStorage
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【中文标题】检查用户是不是已存在于 localStorage【英文标题】:Check if user is already existed in localStorage检查用户是否已存在于 localStorage 【发布时间】:2021-02-11 21:12:12 【问题描述】:const firstName = document.getElementById("firstName");
const lastnName = document.getElementById("lastName");
const email = document.getElementById("newEmail");
const password = document.getElementById("newPassword");
const btnSignup = document.getElementById("btn-signup");
btnSignup.onclick = function () // when mouse click "signup" button
const first_name = firstName.value; // getting the value of firstName and so on..
const last_name = lastName.value;
const e_mail = newEmail.value;
const pass_word = newPassword.value;
if (first_name && last_name && e_mail && pass_word)
//set user input into JSON
let user_data =
firstName: first_name,
lastName: last_name,
email: e_mail,
password: pass_word
//get to localstorage if there is existing user ||or make empty array[]
let clientsArr = JSON.parse(localStorage.getItem('users')) || [];
//ipush ang new user sa array
clientsArr.push(user_data);
//save to localstorage
localStorage.setItem('users', JSON.stringify(clientsArr));
// location.reload();
else if (user_data === localStorage.getItem('users')) // THIS IS THE CODE THAT I AM TRYING
alert("User already existed");
;
我正在尝试在屏幕上显示错误消息或在浏览器上显示警告,此代码确实有效,问题是如何识别本地存储中是否存在现有用户。我想说的是,如果内存中有现有用户,您的“登录”将不接受。谢谢!我对要运行的代码添加了注释。
【问题讨论】:
试试这样的if (localStorage.getItem("user") === null) // your code goes here
【参考方案1】:
几点:
javascript 通过内存引用(RAM 上的位置)比较对象。let
变量绑定到词法范围
。因此,user_data
在第二个 else if
语句中将不可用。
奖励:使用提前退出来保持代码干净。
使用唯一标识符,例如id
。在示例中,我将对象转换为字符串并进行比较。
// Fields
const firstName = document.getElementById("firstName");
const lastnName = document.getElementById("lastName");
const email = document.getElementById("newEmail");
const password = document.getElementById("newPassword");
// Button
const btnSignup = document.getElementById("btn-signup");
function signUp()
const first_name = firstName.value;
const last_name = lastName.value;
const e_mail = newEmail.value;
const pass_word = newPassword.value;
// If either of the values is empty
if (!first_name || !last_name || !e_mail || !pass_word)
return;
//set user input into JSON
let user_data =
firstName: first_name,
lastName: last_name,
email: e_mail,
password: pass_word
// convert to string
let user_data_str = JSON.stringify(user_data)
//get to localstorage if there is existing user ||or make empty array[]
let clientsArr = JSON.parse(localStorage.getItem('users')) || [];
// Convert to string
// Search the list if
const userExists = clientsArr.find(user => JSON.stringify(user) === user_data_str);
if (userExists)
return alert('User already exists')
//ipush ang new user sa array
clientsArr.push(user_data);
//save to localstorage
localStorage.setItem('users', JSON.stringify(clientsArr));
// Attach listener
btnSignup.addEventListener('click', signUp);
<input id="firstName" />
<input id="lastName" />
<input id="newEmail" />
<input id="newPassword" />
<button id="btn-signup">Sign up</button>
【讨论】:
它正在工作!谢谢亚当!我可以再问一次,如果用户尝试将电子邮件和密码登录到登录页面怎么办?问太多了吗?谢谢。 亚当,我的意思是,如果本地存储中的数据将在“登录表单”中使用怎么办? 我建议为此使用后端数据库。我的假设是您这样做是为了练习;可以将LocalStorage
视为数据库。 :)【参考方案2】:
如果您在添加到 localStorage 中的“用户”之前尝试检查用户是否已经存在,您可以执行以下操作:
const firstName = document.getElementById("firstName");
const lastnName = document.getElementById("lastName");
const email = document.getElementById("newEmail");
const password = document.getElementById("newPassword");
const btnSignup = document.getElementById("btn-signup");
btnSignup.onclick = function ()
const first_name = firstName.value;
const last_name = lastName.value;
const e_mail = newEmail.value;
const pass_word = newPassword.value;
// Only get localstorage item once
let clientsArr = JSON.parse(localStorage.getItem('users')) || [];
// Only execute those lines if we have the data that we need
if (first_name && last_name && e_mail && pass_word)
let user_data =
firstName: first_name,
lastName: last_name,
email: e_mail,
password: pass_word
// Check if the user already exists to show an alert or add it to the list
if(clientsArr.includes(user_data))
alert("User already existed");
else
clientsArr.push(user_data);
localStorage.setItem('users', JSON.stringify(clientsArr));
;
【讨论】:
谢谢Casana,我会试试这个,像我这样的初学者请耐心等待,上帝保佑!以上是关于检查用户是不是已存在于 localStorage的主要内容,如果未能解决你的问题,请参考以下文章
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