使用WebStorage 总是报错，求大神帮我看一下。谢谢?报错

报错：Uncaught TypeError: localStorage.setItem is not a function

代码：

var so_localStorage = {
//判断是否支持localStoreage
check: function () {
if (window.localStorage) return true;
else return false;
},
set: function (key, value) {
localStorage.setItem(key, JSON.stringify(value));
},
get: function (key) {
return localStorage.getItem(key);
},
remove: function (key) {
localStorage.removeItem(key);
},
clear: function () {
localStorage.clear();
}
}


var so_sessionStorage = {
//判断是否支持sessionStoreage
check: function () {
if (window.sessionStorage) return true;
else return false;
},
set: function (key, value) {
sessionStorage.setItem(key, value);
},
get: function (key) {
return sessionStorage.getItem(key);
},
remove: function (key) {
sessionStorage.removeItem(key);
},
clear: function () {
sessionStorage.clear();
}
}

调用：

function localStorage(){
so_localStorage.set("ls_test","hello world");
}

function sessionStorage(){
so_sessionStorage.set("ls_test","hello world");
}

关键网上也查不太到....

再次感谢！