normalize_offsets.js

const normalize_offsets = offsets => {
	let arr = offsets.slice();
	if (arr[0] === undefined) arr[0] = 0;
	if (arr[arr.length - 1] === undefined) arr[arr.length - 1] = 1;
	let i = 0, j, start, start_offset, increment;
	while (i < arr.length) {
		if (arr[i] === undefined) {
			start = i;
			start_offset = arr[i - 1];
			j = i;
			while (arr[++j] === undefined);
			increment = (arr[j] - start_offset) / (j - i + 1);
			while (i < j) {
				arr[i] = start_offset + (i - start + 1) * increment;
				i++;
			}
		}
		i++;
	};
	return arr;
}