如何检查存储项是否已设置？

Question

如何检查项目是否已设置localStorage？目前我正在使用

if (!(localStorage.getItem("infiniteScrollEnabled") == true || localStorage.getItem("infiniteScrollEnabled") == false)) {
    // init variable/set default variable for item
    localStorage.setItem("infiniteScrollEnabled", true);
}

Answer 1

getItemWebStorage规范中的方法,null如果该项不存在,则显式返回:

...如果给定键与对象关联的列表中不存在,则此方法必须返回null....

所以你可以:

if (localStorage.getItem("infiniteScrollEnabled") === null) {
  //...
}

看到这个相关的问题:

• 在HTML5 localStorage中存储对象

Answer 2

您可以使用hasOwnProperty方法来检查这一点

> localStorage.setItem('foo', 123)
undefined
> localStorage.hasOwnProperty('foo')
true
> localStorage.hasOwnProperty('bar')
false

适用于当前版本的Chrome(Mac),Firefox(Mac)和Safari.

Answer 3

最短的方法是使用默认值,如果密钥不在存储中:

var sValue = localStorage['my.token'] || ''; /* for strings */
var iValue = localStorage['my.token'] || 0; /* for integers */

Answer 4

有几种方法可以检查我在这里添加它们

方法一

if("infiniteScrollEnabled" in localStorage){
     console.log("Item exists in localstorage");
}else{
    console.log("Item does not exist in localstoarge";
}

方法二

if(localStorage.getItem("infiniteScrollEnabled") === null){
    console.log("Item does not exist in localstoarge";
}else{
   console.log("Item exists in localstorage");
}

方法三

if(typeof localStorage["cart"] === "undefined"){
    console.log("Item does not exist in localstoarge";
}else{
   console.log("Item exists in localstorage");
}

方法4

if(localStorage.hasOwnProperty("infiniteScrollEnabled")){
     console.log("Item exists in localstorage");
 }else{
    console.log("Item does not exist in localstoarge";
 }

Answer 5

if(!localStorage.hash) localStorage.hash = "thinkdj";

或者

var secret =  localStorage.hash || 42;

Answer 6

可以尝试这样的事情：

 let x = localStorage.getItem('infiniteScrollEnabled') === null ? "not found" : localStorage.getItem('infiniteScrollEnabled')