JavaScript Callback Error Prevention Snippets

Here are practical, ready-to-use code snippets to prevent "undefined is not a function" errors when working with JavaScript callbacks.

Safe Callback Executor #

A utility function that safely executes callbacks with built-in error handling:

Callback Validator #

A simple function to validate callbacks before use:

function isValidCallback(callback) {
  return typeof callback === 'function';
}

function validateCallback(callback, defaultFn = () => {}) {
  return isValidCallback(callback) ? callback : defaultFn;
}

// Usage
function processData(data, callback) {
  const validCallback = validateCallback(callback, (result) => 
    console.log('Default handler:', result)
  );
  
  const result = data * 2;
  validCallback(result);
}

Callback Queue Manager #

A snippet for managing multiple callbacks safely:

Method Binding Helper #

Safely bind object methods for use as callbacks:

Async Callback Handler #

Handle both sync and async callbacks safely:

async function safeAsyncCallback(callback, ...args) {
  if (typeof callback !== 'function') {
    return Promise.resolve(null);
  }
  
  try {
    const result = callback(...args);
    
    // Handle both sync and async callbacks
    if (result instanceof Promise) {
      return await result;
    }
    return result;
  } catch (error) {
    console.error('Async callback error:', error);
    return null;
  }
}

// Usage
async function processAsync(data, callback) {
  const result = await safeAsyncCallback(callback, data);
  console.log('Async result:', result);
}

Event Callback Registry #

A robust event system with callback validation:

Callback Timeout Wrapper #

Add timeout protection to callbacks:

function withTimeout(callback, timeoutMs = 5000) {
  if (typeof callback !== 'function') {
    return () => Promise.reject(new Error('Invalid callback'));
  }
  
  return (...args) => {
    return Promise.race([
      new Promise((resolve, reject) => {
        try {
          const result = callback(...args);
          resolve(result);
        } catch (error) {
          reject(error);
        }
      }),
      new Promise((_, reject) => 
        setTimeout(() => reject(new Error('Callback timeout')), timeoutMs)
      )
    ]);
  };
}

// Usage
const slowCallback = withTimeout((data) => {
  // Simulate slow operation
  return new Promise(resolve => setTimeout(() => resolve(data), 1000));
}, 2000);

Callback Chain Builder #

Build safe callback chains:

Quick Copy-Paste Solutions #

For immediate use in your projects:

// Simple callback safety check
const call = (fn, ...args) => typeof fn === 'function' ? fn(...args) : undefined;

// Default callback provider
const withDefault = (callback, defaultFn = () => {}) => 
  typeof callback === 'function' ? callback : defaultFn;

// Callback existence check
const hasCallback = (callback) => typeof callback === 'function';

// Safe method caller
const callMethod = (obj, method, ...args) => 
  obj && typeof obj[method] === 'function' ? obj[method](...args) : undefined;

These snippets provide robust, reusable solutions to prevent "undefined is not a function" errors in your JavaScript callback handling code.