Diff Checker for TypeScript Developers

import { diffLines, Change } from 'diff'; // npm install diff @types/diff

function diffText(original: string, modified: string): void {
  const changes: Change[] = diffLines(original, modified);
  changes.forEach(({ added, removed, value }) => {
    const prefix = added ? '+ ' : removed ? '- ' : '  ';
    value.split('\n').filter(Boolean).forEach(line =>
      console.log(`${prefix}${line}`)
    );
  });
}

// Count changed lines
function countChanges(a: string, b: string): { added: number; removed: number } {
  const changes = diffLines(a, b);
  return {
    added: changes.filter(c => c.added).reduce((n, c) => n + (c.count ?? 0), 0),
    removed: changes.filter(c => c.removed).reduce((n, c) => n + (c.count ?? 0), 0),
  };
}