How to fix TypeError: Argument must be a valid hex string in Node.js

const hexString = "1a2b"; // Valid - 4 characters (2 bytes)
const invalid = "1a2";   // Invalid - 3 characters (odd)

if (hexString.length % 2 !== 0) {
  console.error("Hex string has odd length:", hexString.length);
}

const hexString = "1a2";
const padded = hexString.padStart(hexString.length + 1, "0"); // "01a2"
const buffer = Buffer.from(padded, "hex");

const hexRegex = /^[0-9a-fA-F]*$/;
const hexString = "1a2bZZ"; // Contains invalid characters Z, Z

if (!hexRegex.test(hexString)) {
  console.error("Hex string contains invalid characters");
}

const validHex = "1a2b3c"; // Valid
const buffer = Buffer.from(validHex, "hex");

const rawInput = "  1a 2b 3c  "; // From external source
const normalized = rawInput.trim().replace(/\s+/g, "").toLowerCase();

if (normalized.length % 2 !== 0) {
  throw new Error("Invalid hex string length");
}

const buffer = Buffer.from(normalized, "hex");
console.log(buffer); // <Buffer 1a 2b 3c>

function safeHexToBuffer(hexString) {
  const cleaned = hexString.trim().replace(/\s+/g, "").toLowerCase();
  
  // Validate length
  if (cleaned.length % 2 !== 0) {
    throw new Error("Hex string must have even length");
  }
  
  // Validate characters
  if (!/^[0-9a-f]*$/.test(cleaned)) {
    throw new Error("Hex string contains invalid characters");
  }
  
  return Buffer.from(cleaned, "hex");
}

// Usage
try {
  const buffer = safeHexToBuffer("1a2b3c");
  console.log("Success:", buffer);
} catch (err) {
  console.error("Invalid hex:", err.message);
}

const fromAPI = '"1a2b3c"'; // With quotes
const rawData = fromAPI.slice(1, -1); // Remove quotes

console.log("Raw data length:", rawData.length);
console.log("Raw data:", JSON.stringify(rawData));
console.log("Character codes:", [...rawData].map(c => c.charCodeAt(0)));

const buffer = Buffer.from(rawData, "hex");