How to Check If Function Exists in Javascript?

How to check if function exists in JavaScript?

When working with JavaScript, it is common to come across situations where you need to check if a function exists before calling it. This can be especially useful when working with third-party libraries or when dealing with dynamically loaded scripts. In this blog post, we will explore multiple solutions to this problem.

Solution 1: Using the typeof operator

The typeof operator in JavaScript allows you to determine the type of a variable or expression. By using typeof on a function, you can check if it exists.

if (typeof functionName === 'function') {
  // Function exists, call it
  functionName();
} else {
  // Function does not exist
  console.log('Function does not exist');
}

This solution works by checking if the type of the variable functionName is ‘function’. If it is, the function exists and can be called. Otherwise, an error message is logged to the console.

Solution 2: Using the in operator

The in operator in JavaScript allows you to check if a property exists in an object. By using in on the global object (window in browsers), you can check if a function exists.

if ('functionName' in window) {
  // Function exists, call it
  window.functionName();
} else {
  // Function does not exist
  console.log('Function does not exist');
}

This solution works by checking if the property functionName exists in the global object (window). If it does, the function exists and can be called. Otherwise, an error message is logged to the console.

Solution 3: Using the try…catch statement

The try…catch statement in JavaScript allows you to catch and handle errors. By wrapping the function call in a try block, you can check if the function exists.

try {
  functionName();
  // Function exists, call it
} catch (error) {
  // Function does not exist
  console.log('Function does not exist');
}

This solution works by attempting to call the function inside a try block. If the function exists, it will be called without any errors. Otherwise, the catch block will be executed, and an error message is logged to the console.

These are three different solutions to check if a function exists in JavaScript. Depending on your use case, you can choose the one that suits you best. Remember to always handle cases where the function does not exist to avoid unexpected errors.

How to Check If Function Exists in Javascript?