localStorageGetSpace.js

// localStorageGetSpace.js v1, https://stackoverflow.com/questions/4391575/how-to-find-the-size-of-localstorage
function localStorageGetSpace(number = false) {
	let allStrings = '';
	for (let key in window.localStorage) {
		if (window.localStorage.hasOwnProperty(key)) {
			allStrings += window.localStorage[key];
		};
	};
	allStrings = allStrings ? 3 + ((allStrings.length * 16) / 8192) : 0;
	if (number == true) {
		return allStrings;
	} else if (typeof formatBytes != 'undefined') {
		return formatBytes(allStrings);
	} else {
		return allStrings + ' KB';
	};
};

localStorageGetSpace.min.js

// localStorageGetSpace.min.js v1
function localStorageGetSpace(a=!1){let b='';for(let c in window.localStorage)window.localStorage.hasOwnProperty(c)&&(b+=window.localStorage[c]);return b=b?3+16*b.length/8192:0,!0==a?b:'undefined'==typeof formatBytes?b+' KB':formatBytes(b)}