Javascript: get localStorage maximum size

fiddle.js

if (!localStorage) {
    console.log('unavailable');
} else {
    var max = 'x', s;
    var lower_bound = 1, upper_bound = 1, middle;

    // determine lower and upper bound
    try {
        while (true) {
            localStorage.setItem('test', max);
            lower_bound = upper_bound;
            upper_bound *= 2;
            max = max + max;
        }
    } catch (e) {
    }

    // do a binary search
    while (upper_bound - lower_bound > 2) {
        try {
            middle = (lower_bound + upper_bound) / 2;
            s = max.substr(0, middle);
            localStorage.setItem('test', s);
            lower_bound = middle;
        } catch (e) {
            upper_bound = middle;
        }
    }

    console.log('size=' + lower_bound + '/' + upper_bound + '=' + (lower_bound / 1024).toFixed(1) + 'k');
}