What is the max size of localStorage values?

Here's a straightforward script for finding out the limit:

if (localStorage && !localStorage.getItem('size')) {

    var i = 0;

    try {

        // Test up to 10 MB

        for (i = 250; i <= 10000; i += 250) {

            localStorage.setItem('test', new Array((i * 1024) + 1).join('a'));

        }

    } catch (e) {

        localStorage.removeItem('test');

        localStorage.setItem('size', i - 250);            

    }

}

The script will test setting increasingly larger strings of text until the browser throws and exception. At that point it’ll clear out the test data and set a size key in localStorage storing the size in kilobytes.

4 years ago

You don't want to stringify large objects into a single localStorage entry. That would be very inefficient - the whole thing would have to be parsed and re-encoded every time some slight detail changes. Also, JSON can't handle multiple cross references within an object structure and wipes out a lot of details, e.g. the constructor, non-numerical properties of arrays, what's in a sparse entry, etc.

Instead, you can use Rhaboo. It stores large objects using lots of localStorage entries so you can make small changes quickly. The restored objects are much more accurate copies of the saved ones and the API is incredibly simple. E.g.:

var store = Rhaboo.persistent('Some name');

store.write('count', store.count ? store.count+1 : 1);

store.write('somethingfancy', {

  one: ['man', 'went'],

  2: 'mow',

  went: [  2, { mow: ['a', 'meadow' ] }, {}  ]

});

store.somethingfancy.went[1].mow.write(1, 'lawn');

4 years ago

I wrote this simple code that is testing localStorage size in bytes.

const check = bytes => {

  try {

    localStorage.clear();

    localStorage.setItem('a', '0'.repeat(bytes));

    localStorage.clear();

    return true;

  } catch(e) {

    localStorage.clear();

    return false;

  }

};

4 years ago