为什么警告（ty​​peof pageViewCount）;它显示＆＃34;数字＆＃34;，同时警告（pageViewCount）;它显示＆＃34; NaN＆＃34;？

Question

＆＃34; typeof pageViewCount＆＃34;显示＆＃34;数字＆＃34;而＆＃34; pageViewCount＆＃34;显示＆＃34; NaN＆＃34;但我不知道为什么。 代码如下所示。

var pageViewCount = localStorage.getItem("pageViewCount");
var pageFirstVisited = localStorage.getItem("pageFirstVisited");
var now = new Date();
if(pageViewCount == null){
    pageViewCount = 0;
    pageFirstVisited = now.toUTCString();
}
var oneMonth = new Date(pageFirstVisited);
oneMonth.setMonth(oneMonth.getMonth()+1);
if(now>oneMonth){
    pageViewCount = 0;
    pageFirstVisited = now.toUTCString();
}
pageViewCount = parseInt("pageViewCount",10)+1;
alert(pageViewCount);
localStorage.setItem("pageViewCount",pageViewCount);
localStorage.setItem("pageFirstVisited",pageFirstVisited);
var output = "You've visited this page " + pageViewCount + " times since" + pageFirstVisited;
document.write(output); 

Answer 1

你正在使用parseInt()

的刺痛

pageViewCount = parseInt("pageViewCount",10)+1;

您应该将其更改为

pageViewCount = parseInt(pageViewCount,10) + 1;

Answer 2

基本上，NaN是一个数值数据类型值，它告诉数字值不可计算或可显示。 https://en.wikipedia.org/wiki/NaN