Example localstorage

du.localstorage

env = [
{
    "name": "Výdaje",
    "color": "#ffffff"
}
]
env_saved = localStorage['envelopes'];
if (env_saved !== undefined ) {
    envelopes = JSON.parse(env_saved); 
    _env = [], e = []
    for (var i = 0; i < envelopes.length; i++) {
      _env = 
          {
              "name": envelopes[i].name+"_add",
              "color": envelopes[i].color
          }
      e.push(_env);
    };
    e.push(env[0]);
    localStorage['envelopes'] = JSON.stringify(e);
} else {
    localStorage['envelopes'] = JSON.stringify(env);
}
 
console.log(localStorage['envelopes'])
 
var localStorageSpace = function() {
    var allStrings = '';
    for(var key in window.localStorage){
        if(window.localStorage.hasOwnProperty(key)){
            allStrings += window.localStorage[key];
        }
    }
    return allStrings ? 3 + ((allStrings.length*16)/(8*1024)) + ' KB' : 'Empty (0 KB)';
    };
 
console.log(localStorageSpace());
localStorage.removeItem('envelopes');