如何檢查本地存儲中的鍵值？

Question

如果密鑰中沒有預先存儲的值，則用戶只能存儲信息。 如何檢查是否已經存在值，並提醒用戶已經存在值？ 我知道我必須使用if語句。 如果有值，請警告用戶。 其他設置項...（保存對象）。 但是我該如何檢查價格呢？

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;
}

Answer 1

我認為以下代碼段可以為您提供幫助！

var getObj = localStorage.getItem('announcement');
var obj = JSON.parse(getObj);
for (key in obj) {
  if(obj[key] !== ''){
   alert(key + 'is existed');
  }else{
   var newValue = document.getElementById(key).value;
   obj[key] = newValue == '' ? '' : newValue;
  }
}
var newObjS = JSON.stringify(obj);

localStorage.setItem('announcement', newObjS);