localStorage['root2']=null;

localStorage.getItem("root2") === null //false

也许最好先看一遍计划?

localStorage['root1']=187;
187
'root1' in localStorage
true

我在这里添加了一些方法来检查

方法1

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

方法2

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

方法3

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";
 }

最短的方法是使用默认值，如果key不在存储中:

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

WebStorage规范中的getItem方法，如果项不存在，则显式返回null:

．.． 如果给定的键在与该对象关联的列表中不存在，则该方法必须返回null. ...

所以，你可以:

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

请看这个相关问题:

在HTML5 localStorage中存储对象

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

Or

var secret =  localStorage.hash || 42;

正如@Christian C. Salvadó上面提到的，你可以做到 If (xxx === null){}

但是null也是一个假值，就像这样:

if (null){
console.log ("hello");
}

它不打印“hello”。