Check Whether a JavaScript String Is Empty: State the Whitespace Rule

The task

Accept a nonblank string label after trimming its ends. Keep internal spaces, and return null for unsupported values rather than treating them as labels.

Runnable Node 22 example

const assert = require('node:assert/strict');

function label(value) {
  if (typeof value !== 'string') return null;
  const cleaned = value.trim();
  return cleaned.length === 0 ? null : cleaned;
}
assert.equal('' === '', true);
assert.equal('   ' === '', false);
assert.equal(label('   '), null);
assert.equal(label(null), null);
assert.equal(label(undefined), null);
assert.equal(label('  east  wing  '), 'east  wing');
console.log(JSON.stringify(['', '   ', null, '  east  wing  '].map(label)));

Expected output and explanation

The strict empty-string comparison rejects only zero-length text; three spaces are still a string with content. The helper deliberately adopts a stronger rule and checks the trimmed result. It retains the two interior spaces in east wing because this contract only trims the ends.

Null and undefined fail the type guard before trim runs. That keeps the input contract explicit instead of converting every value with String and accidentally accepting the text “null” as a meaningful label.

Pitfall to check

Do not reuse this normalization for every field. Passwords, fixed-width records and other inputs can treat whitespace differently. If the product needs a maximum length, specify its counting unit separately rather than assuming nonblank also means valid.