document.getElementById('validateBtn').addEventListener('click', validate); // optional live validation: // document.getElementById('expr').addEventListener('input', validate); </script> </body> </html> If you need to generate the file on the fly (e.g., a PDF ruler with custom branding), a simple endpoint could be:
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function parseAndEval(str) // keep only digits, dot, hyphen, and optionally leading/trailing spaces const clean = str.trim(); const parts = clean.split('-'); if (parts.length !== 3) return null; const nums = parts.map(p => parseFloat(p)); if (nums.some(isNaN)) return null; // left‑to‑right subtraction: a - b - c return nums[0] - nums[1] - nums[2]; x-x-x is equal to 2 5 meter download link