How to Check If a Function Exists in JavaScript

by

To check if a function exists in JavaScript, you can use the “typeof” operator.

Example 1

function mainFunction() {
  console.log('Hello, world!');
}

if (typeof mainFunction === 'function') {
  mainFunction(); // Calls the function if it exists
} else {
  console.log('The function does not exist.');
}

Output

In this example, typeof mainFunction will return the string ‘function’ if mainFunction is a function.

If it’s not a function or not defined, the typeof mainFunction will return a different string (e.g., ‘undefined’ or ‘object’).

By checking if typeof mainFunction === ‘function’, you can ensure that you only call the function if it exists.

If you’re working with object methods or functions in a particular namespace, you can use a similar approach.

Example 2

const mainObject = {
  mainMethod: function () {
    console.log('Hello, world!');
  },
};

if (typeof mainObject.mainMethod === 'function') {
  mainObject.mainMethod(); // Calls the method if it exists
} else {
  console.log('The method does not exist.');
}

Output

In this example, the function mainMethod is a property of the mainObject object.

By checking if typeof mainObject.mainMethod === ‘function’, you can ensure that you only call the method if it exists.

Leave a Comment