isRotattion.js

/*
Assume you have a method isSubstring which checks if one word is a substring of
another. Given two strings, s1 and s2, write code to check if s2 is a rotation of s1 using
only one call to isSubstring (i.e., “waterbottle” is a rotation of “erbottlewat”).
*/
function isRotation(str1, str2) {
	if(str1.length > 0 && str1.length === str2.length) {
		var concatStr = str1 + str1;
		return concatStr.indexOf(str2) !== -1;
	}
	return false;
}