localstorage.js

const isJson = (str) => {
    try { JSON.parse(str); }
    catch (e) { return false; }
}

export default localstorage = {
    listAll: () => Object.keys(localStorage),
    getAll: () => localstorage.get(localstorage.listAll()),
    get: (key) => {
        if (Array.isArray(key)) {
            const object = {};
            for(const item of key) object[item] = localstorage.get(item);
            return object;
        } else if (typeof key === "string") {
            const value = localStorage.getItem(key);
            return (isJson(value)) ? JSON.parse(value) : value;
        }
    },
    save: (key, value) => {
        if (typeof key === "object")
            for (const item of Object.keys(key))
                localstorage.save(item, key[item]);
        else if (typeof key === "string")
            localStorage.setItem(key, (isJson(value)) ? JSON.stringify(value) : value);
    },
    remove: (key) => (typeof key === "string") ? localStorage.removeItem(key) : key.map(k => localstorage.remove(k)),
};

localstorage.min.js

const isJson=(str)=>{try{JSON.parse(str)}catch(e){return!1}}
const localstorage={listAll:()=>Object.keys(localStorage),getAll:()=>localstorage.get(localstorage.listAll()),get:(key)=>{if(Array.isArray(key)){const object={};for(const item of key)object[item]=localstorage.get(item);return object}else if(typeof key==="string"){const value=localStorage.getItem(key);return(isJson(value))?JSON.parse(value):value}},save:(key,value)=>{if(typeof key==="object")for(const item of Object.keys(key))localstorage.save(item,key[item]);else if(typeof key==="string")localStorage.setItem(key,(isJson(value))?JSON.stringify(value):value)},remove:(key)=>(typeof key==="string")?localStorage.removeItem(key):key.map(k=>localstorage.remove(k)),}

Use Cases:

localstorage.listAll(); // list all keys
localstorage.getAll(); // get all keys
localstorage.get("key"); // return one value
localstorage.get(["key1", "key2"]); // return object of values
localstorage.save("key", "value"); // save one value
localstorage.save({"key1": "value1", "key2": "value2"}); // save multiple values
localstorage.remove("key"); // remove one value
localstorage.remove(["key1", "key2"]); // remove multiple values