Fix JavaScript TypeError: X is not a function (2025 Guide)

Fix TypeError: X is not a function in JavaScript - 2025 Guide

Posted on: March 12, 2025

If you’ve ever seen the error "TypeError: 'X' is not a function" in JavaScript, you’re not alone. It’s one of the most common issues developers face, especially when working with functions or libraries. In this quick guide, I’ll explain why this error happens and show you how to fix it in minutes.

What Causes "TypeError: 'X' is not a function"?

This error occurs when JavaScript expects a function but gets something else—like undefined, a string, or an object. Here are the top reasons:

• Typo in Function Name: You mistyped the function name.
• Missing Library: A library (like jQuery) isn’t loaded properly.
• Wrong Scope: The function isn’t available where you’re calling it.

Check out this interactive example (open your browser console with F12 to see the error):

In this example, myVar is a string, not a function, so calling it with () triggers the error.

How to Fix It: 3 Solutions

Here’s a step-by-step process to resolve this error:

(Diagram: Developer runs code, gets error, checks typo/library/variable, fixes issue.)

Solution 1: Check for Typos

Make sure you’re calling the correct function name. For example:

// Wrong
function sayHello() {
  console.log("Hi!");
}
sayHelo(); // TypeError: sayHelo is not a function

// Fixed
sayHello(); // Works fine

Double-check your spelling—it’s a simple but common mistake!

Solution 2: Verify Library Loading

If you’re using a library like jQuery, ensure it’s loaded before your code runs. Example:

<script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
<script>
  $(document).ready(function() {
    console.log("Ready!");
  });
</script>

If $ or another library method fails, check the <script> order or CDN link.

Solution 3: Debug the Variable

If a variable should hold a function but doesn’t, log it to see what’s wrong:

// Wrong
const myFunc = { name: "test" };
myFunc(); // TypeError: myFunc is not a function

// Fixed
const myFunc = () => console.log("Works!");
myFunc(); // Output: Works!

Use console.log(typeof myFunc) to confirm it’s a function before calling it.

Quick Checklist

• Is the function spelled correctly?
• Are all libraries loaded?
• Is the variable actually a function? (Check with typeof.)

Conclusion

The "TypeError: 'X' is not a function" error is frustrating but easy to fix once you know where to look. Whether it’s a typo, a loading issue, or a scope problem, these steps will get you back on track. Got another JavaScript error bothering you? Let me know in the comments!

Comments

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