Function that given a sorted array of page numbers, returns a string representing a book index. Combines consecutive pages to create ranges. Given [1,3,4,5,7,8,10] it should return the string “1, 3-5, 7-8, 10”.

bookIndex.js

var arr = [1,2,3,5,8,10,11,12,15]

function bookIndex(arr) {
	var temp = [];
	for (var i = 0; i < arr.length; i++) {
		if (arr[i]+1 == arr[i+1]) {
			var start = arr[i];
			while (arr[i]+1 == arr[i+1]) {
				i++;
			}
		var end = arr[i];
		temp.push(start + "-" + end);
		} else {
			temp.push(arr[i]);
		}
	}
	var newstring = temp.join(',');
	return newstring
}

console.log(bookIndex(arr));