binarySearchStorageCapacity.html

<script>
function log(s) {
	document.writeln(s+"<br>");
	console.log(s);
}


function generateString(bytes) {
	return Array(bytes+1).join("a");
}

function binarySearch(boolFn, min, max) {
	var mid = ((max + min) / 2)|0;
	if(mid == min) return mid;
	if(boolFn(mid)) return binarySearch(boolFn, mid, max);
	else return binarySearch(boolFn, min, mid);
}

// test is between num/2 and nu
function binaryBracketSearch(test) {
	var num = 1;
	while(test(num)) num *= 2;
	return num;
}

function test(num) {
	log("testing "+num + " bytes (2^"+Math.log2(num)+")");
	try {
		localStorage.setItem("a", generateString(num));
		localStorage.removeItem("a");
	} catch(e) {
		return false;
	}
	return true;
}
max = binaryBracketSearch(test);
log("result: "+binarySearch(test, (max/2)|0, max));
</script>