levenshtein distance (Edit distance) algorithm in typescript

levenshtein.ts

function levenshtein(a: string, b: string): number {
	if (a.length == 0) {
		return b.length;
	}
	if (b.length == 0) {
		return a.length;
	}
	const matrix = new Array<number[]>(b.length + 1);
	for (let i = 0; i <= b.length; i++) {
		matrix[i] = new Array<number>(a.length + 1);
		matrix[i][0] = i;
	}
	for (let i = 1; i <= b.length; ++i) {
		for (let j = 1; j <= a.length; ++j) {
			matrix[i][j] = (b[i - 1] === a[j - 1]) ? 
				matrix[i - 1][j - 1] 
				: 
				Math.min(
					matrix[i - 1][j - 1], // substitution
					matrix[i][j - 1], // insertion
					matrix[i - 1][j] // deletion
				) + 1;
		}
	}
	return matrix[b.length][a.length];
}