just a neat solution we found to a challenge

FindLowestMissingPositive.ts

/**
 * Finds the lowest missing positive number in an array of numbers (quite efficiently).
 */
function findLowestMissingPositive(subject: Array<number>): number {
	/** 
	 * The iterator, which will be the lowest missing number after the loop.
	 */
	let x = -1; // start at -1 because we increment it before the first check
	while (1) { // 1 = true
		if (!subject.includes(++x)) { break; } // break if the next number isn't in the subject
	}
	return x; // since we started with 0 and ended with up to 1 more than the length of the subject, this will be the lowest missing number
}