Generate random base62 string the right way using window.crypto

random.js

random = function(length) {
	var base = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'.split('');
	var array = new Uint8Array(length);
	window.crypto.getRandomValues(array);
	var str = '';
	for (var i = 0; i < array.length; i++) {
		str += base[array[i]%base.length];
	};
	return str;
}