Debugging "TypeError: X is not a function" in JavaScript

Debugging “TypeError: X is not a function” in JavaScript

Debugging “TypeError: X is not a function” in JavaScript

In this post, we will give you information about Debugging “TypeError: X is not a function” in JavaScript. Here we will give you detail about Debugging “TypeError: X is not a function” in JavaScript And how to use it also give you a demo for it if it is necessary.

The TypeError: X is not a function error is a common cause of confusion for JavaScript beginners.
JavaScript throws this error when you attempt to call a value that isn’t a function. For example:

const x = 42;

x(); // Throws 'TypeError: x is not a function'

Most modern JavaScript runtimes are good about formatting this error, so you know what expression you tried to call that isn’t a function. For example, another common cause of
this error is calling a non-existant method on an object.

const moment = require('moment');

const date = moment('2020-06-01');

// Typo! Throws 'TypeError: date.formt is not a function'

If JavaScript throws this error in code that you wrote, you should double check the code at the line number
in the error’s stack trace. Odds are, you either typo-ed, or you need to add a check to make sure the value
that you’re calling is a function.

// Ensure that 'x' is a function to avoid TypeError.
if (typeof x !== 'function') {


A Note on Semicolons

If you don’t use semicolons, you can get some surprising instances of this error. For example, the below
code throws TypeError: arr[0] is not a function:

const arr = []

const val = arr[0]
(function() { console.log(val) })()

Because there isn’t a semicolon at the end of arr[0], JavaScript treats the above code as equivalent to:

const arr = []

const val = arr[0](function() { console.log(val) })()

If you write JavaScript without semicolons, be sure to use a linter to avoid mistakes like this!

JavaScript Fundamentals for Debugging “TypeError: X is not a function” in JavaScript

JavaScript is a programming language that is used to create interactive web pages. It is a client-side scripting language, which means that it runs on the user’s browser. JavaScript can be used to add animation, interactivity, and functionality to web pages.

Here are some of the fundamentals of JavaScript:

  • Variables: Variables are used to store data. They are declared using the var keyword.
  • Data types: JavaScript has a variety of data types, including strings, numbers, booleans, objects, and arrays.
  • Operators: Operators are used to perform operations on data.
  • Control flow statements: Control flow statements allow you to control the order in which your code is executed.
  • Functions: Functions are blocks of code that can be reused.
  • Objects: Objects are used to store data in key-value pairs.
  • Arrays: Arrays are used to store data in a sequential order.
  • Events and event handlers: Events are notifications that are sent by the browser when something happens, such as when the user clicks on an element or moves the mouse over an element. Event handlers are functions that are called in response to an event.
  • DOM manipulation: The Document Object Model (DOM) is a tree-like structure that represents the elements of a web page. JavaScript can be used to manipulate the DOM to change the appearance or behavior of a web page.

These are just some of the fundamentals of JavaScript. There are many other concepts that you can learn as you continue to develop your skills.

Here are some resources that you can use to learn more about JavaScript:

  • Mozilla Developer Network (MDN): The MDN is a great resource for learning about JavaScript. It has a comprehensive reference guide, tutorials, and articles on a wide range of topics.
  • W3Schools: W3Schools is another great resource for learning about JavaScript. It has interactive tutorials and quizzes that can help you learn the basics of the language.
  • is a website that provides in-depth tutorials on JavaScript. It also has a forum where you can ask questions and get help from other JavaScript developers.

I hope this helps!

Here are some additional tips for learning JavaScript:

  • Start with the basics: Before you start trying to build complex applications, it’s important to learn the basics of JavaScript. This includes things like variables, data types, operators, and control flow statements.
  • Practice regularly: The best way to learn JavaScript is to practice regularly. Try to find some time each day to work on JavaScript projects.
  • Get help from others: If you get stuck, don’t be afraid to ask for help from others. There are many online forums and communities where you can get help from other JavaScript developers.

With a little practice, you’ll be able to learn JavaScript and start building amazing web applications.

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