How to fix TypeError: The 'path' argument must be of type string. Received type number in Node.js

TypeError: The 'path' argument must be of type string. Received type number
    at validatePath (node:internal/fs/utils:168:13)
    at Object.readFile (node:fs/promises:32:18)
    at /path/to/your/file.js:15:22

import { readFile } from 'fs/promises';

let filePath = getUserPath(); // Could be undefined or wrong type
console.log('filePath type:', typeof filePath);
console.log('filePath value:', filePath);

// This might fail if filePath is not a string
const data = await readFile(filePath, 'utf-8');

// ❌ BAD - filePath might be undefined
const filePath = config.path;
await readFile(filePath);

// ✓ GOOD - Provide a default or check for undefined
const filePath = config.path ?? './default.txt';
if (typeof filePath !== 'string') {
  throw new Error('Path must be a string');
}
await readFile(filePath);

// ❌ BAD - Passing a number accidentally
const fileIndex = 5;
const data = await readFile(fileIndex); // Fails: number is not a string

// ✓ GOOD - Convert to string explicitly
const filePath = String(fileIndex); // Converts 5 to '5'
const data = await readFile(filePath);

// ✓ GOOD - Or use string interpolation
const filePath = `file_${fileIndex}.txt`;
const data = await readFile(filePath);

// ✓ GOOD - For arrays, use proper path joining
import { join } from 'path';
const dirName = 'data';
const fileName = 'file.txt';
const filePath = join(dirName, fileName); // Returns 'data/file.txt'
const data = await readFile(filePath);

// ❌ BAD - Destructuring could fail silently
const { filePath } = config;
await readFile(filePath); // filePath is undefined if config lacks this property

// ✓ GOOD - Provide defaults in destructuring
const { filePath = './default.txt' } = config;
if (typeof filePath !== 'string') {
  throw new Error('filePath must be a string');
}
await readFile(filePath);

// ✓ GOOD - Explicit validation
const { filePath } = config;
if (!filePath || typeof filePath !== 'string') {
  throw new Error('Invalid filePath: must be a non-empty string');
}
await readFile(filePath);

import { readFile } from 'fs/promises';

interface Config {
  filePath: string; // Explicitly require string
}

async function loadData(config: Config): Promise<string> {
  // TypeScript will error if filePath is not a string
  const data = await readFile(config.filePath, 'utf-8');
  return data;
}

// ✓ This compiles fine
await loadData({ filePath: './data.txt' });

// ❌ TypeScript error: Type 'number' is not assignable to type 'string'
await loadData({ filePath: 123 });