javascript - 使用JS从LocalStorage加载的问题

Question

//Set Variables
var cookies = 0;
var cursors = 0;
var prestige = 0;
var cursorCookies = cursors * 0.1;
var save = {
    cookies: cookies,
    cursors: cursors,
    prestige: prestige
}

function loadgame(){
var savegame = JSON.parse(localStorage.getItem("save"));
 if (typeof savegame.cookies !== "undefined") cookies = savegame.cookies;
 if (typeof savegame.cursors !== "undefined") cursors = savegame.cursors;
 if (typeof savegame.prestige !== "undefined") prestige = savegame.prestige; 
}
onload(loadgame());

function round(value, decimals) {
  return Number(Math.round(value+'e'+decimals)+'e-'+decimals);
}

function CookieClick(number)
{
  cookies = cookies + number;
  document.getElementById("cookies").innerHTML = round(cookies,2)
}
function buyCursor(){
    var cursorCost = Math.floor(10 * Math.pow(1.1,cursors));     //works out the cost of this cursor
    if(cookies >= cursorCost){                                   //checks that the player can afford the cursor
      cursors = cursors + 1;                                   //increases number of cursors
      cursorCookies = cursors * 0.1;
        cookies = cookies - cursorCost;                          //removes the cookies spent
        document.getElementById('cursors').innerHTML = cursors;  //updates the number of cursors for the user
        document.getElementById('cookies').innerHTML = cookies;  //updates the number of cookies for the user
    }
    var nextCost = Math.floor(10 * Math.pow(1.1,cursors));       //works out the cost of the next cursor
    document.getElementById('cursorCost').innerHTML = nextCost;  //updates the cursor cost for the user
}




window.setInterval(function(){
CookieClick(cursorCookies); 
localStorage.setItem("save",JSON.stringify(save)); 
document.getElementById('saveinfo').innerHTML = "Saved: " + Date();
}, 1000);

这是我第一次使用 javascript 和 localstorage，所以请耐心等待，谢谢:)

我目前正在尝试的只是加载我正在保存的 3 个变量，但有些事情不太顺利。我的测试站点:http://atz-exportforce320313.codeanyapp.com/

感谢您的帮助!

Answer 1

正如我在 Facebook Messenger 中指出的:

如果您访问 localStorage 中尚未创建的变量，.getItem() 将简单地返回 undefined
如果您通过 JSON.parse() 传输 undefined ，它也只会返回 null 。
要解决此问题，您只需在尝试使用 JSON.parse() 之前检查它的响应即可。

一个简单的例子:

var savegame = JSON.parse(localStorage.getItem('save'));
if (savegame === null) {
    // initialize default values here or simply abort further execution
    return;

    // if cookies, cursors and prestige are global variables you can access them through window:
    var variables = ['cookies', 'cursors', 'prestige'];

    variables.forEach(function(name) {
        if (name in savegame) window[name] = savegame[name];
    });
}

现在您还尝试通过此行保存状态:
localStorage.setItem("保存",JSON.stringify(save));
这将不起作用，因为您没有将变量写入 save
您基本上必须首先将它们从全局变量添加到一起，例如:

var variables = ['cookies', 'cursors', 'prestige'];
variables.forEach(function(name) {
    save[name] = window[name];
});
localStorage.setItem('save', JSON.stringify(save));

PS:
一般来说，我不建议在全局范围内定义你的东西