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Levenshtein Edit Distance CLI

A zero-dependency Node CLI that computes the Levenshtein edit distance between two strings, with a rolled one-row dynamic program and unit tests.

node --version

node levenshtein.mjs kitten sitting

node --test levenshtein.test.mjs

Prints the integer edit distance between the two arguments, for example 3 for kitten and sitting.

What it does

Computes the minimum number of single-character insertions, deletions, or substitutions to turn one string into another. The implementation keeps only one row of the dynamic-programming table, so memory is O(min length) instead of O(n*m).

export function levenshtein(a, b) {
  if (a === b) return 0;
  if (a.length === 0) return b.length;
  if (b.length === 0) return a.length;
  let prev = Array.from({ length: b.length + 1 }, (_, j) => j);
  for (let i = 1; i <= a.length; i++) {
    const curr = [i];
    for (let j = 1; j <= b.length; j++) {
      const cost = a[i - 1] === b[j - 1] ? 0 : 1;
      curr[j] = Math.min(curr[j - 1] + 1, prev[j] + 1, prev[j - 1] + cost);
    }
    prev = curr;
  }
  return prev[b.length];
}

const [a, b] = process.argv.slice(2);
if (a === undefined || b === undefined) { console.error('usage: levenshtein <a> <b>'); process.exit(1); }
console.log(levenshtein(a, b));

Run and verify

node levenshtein.mjs kitten sitting

Run the test command to check the implementation: node --test levenshtein.test.mjs.

Expected Output

For kitten and sitting the distance is 3 (k→s, e→i, and insert g). The program prints exactly one integer:

3

Limitations

Operates on UTF-16 code units, so a single emoji or accented grapheme may count as more than one unit. Use a grapheme splitter before calling it if that matters for your input.