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如果沒有存儲到密鑰中的預先存儲的值,用戶應該只能存儲信息。我如何檢查是否已有值,並提醒用戶已有值?我知道我必須使用if語句。如果有值提醒用戶。否則設置項目...(保存對象)。但是,我如何檢查價值?如何檢查本地存儲中的密鑰是否有值?
function addEvent() {
var announcement = {
title: document.getElementById('title').value,
group: document.getElementById('group').value,
author: document.getElementById('author').value,
type: document.getElementById('type').value,
date: document.getElementById('date').value,
time: document.getElementById('time').value,
gender: document.getElementById('gender').value,
grade: document.getElementById('grade').value,
message: document.getElementById('message').value
};
var objS = JSON.stringify(announcement);
localStorage.setItem('announcement', objS);
alert('Announcement successfully stored!');
}
function showA() {
var getObj = localStorage.getItem('announcement');
var objP = JSON.parse(getObj);
document.getElementById('showAnnouncement').innerHTML = "Announcement"+"<br/>Title:"+objP.title+"<br/>Group:"+objP.group+"<br />Author:"+objP.author+"<br />Type:"+objP.type+"<br/>Date:"+objP.date+"<br />Time:"+objP.time+"<br/>Gender:"+objP.gender+"<br/>Grades:"+objP.grade+"<br />Message:"+objP.message;
}