Check if localStorage is available

Question

I know there has been many questions about checking for localStorage but what if someone manually shuts it off in their browser? Here's the code I'm using to check:

localStorage.setItem('mod', 'mod'); if (localStorage.getItem('mod') != null){   alert ('yes');   localStorage.removeItem('mod'); } else {   alert ('no'); } 

Simple function and it works. But if I go into my Chrome settings and choose the option "Don't Save Data" (I don't remember exactly what it's called), when I try to run this function I get nothing but Uncaught Error: SecurityError: DOM Exception 18. So is there a way to check if the person has it turned off completely?

UPDATE: This is the second function I tried and I still get no response (alert).

try {   localStorage.setItem('name', 'Hello World!'); } catch (e) {   if (e == QUOTA_EXCEEDED_ERR) {    alert('Quota exceeded!');   } } 

Answer 1

Use modernizr's approach (you might want to change my function name to something better):

function lsTest(){     var test = 'test';     try {         localStorage.setItem(test, test);         localStorage.removeItem(test);         return true;     } catch(e) {         return false;     } }  if(lsTest() === true){     // available }else{     // unavailable } 

It's not as concise as other methods but that's because it's designed to maximise compatibility.

The original source: https://github.com/Modernizr/Modernizr/blob/master/feature-detects/storage/localstorage.js

Working example: http://jsfiddle.net/6sm54/2/

Answer 2

I'd check that localStorage is defined prior to any action that depends on it:

if (typeof localStorage !== 'undefined') {     var x = localStorage.getItem('mod'); } else {     // localStorage not defined } 

UPDATE:

If you need to validate that the feature is there and that it is also not turned off, you have to use a safer approach. To be perfectly safe:

if (typeof localStorage !== 'undefined') {     try {         localStorage.setItem('feature_test', 'yes');         if (localStorage.getItem('feature_test') === 'yes') {             localStorage.removeItem('feature_test');             // localStorage is enabled         } else {             // localStorage is disabled         }     } catch(e) {         // localStorage is disabled     } } else {     // localStorage is not available }