According to the [ Mozilla website](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError) for developer documents, *"**the TypeError object** represents an error when a value is not of the expected type."* **Uncaught** means that the error was not caught in the catch part of the try-catch block.

![](/api/edpresso/shot/4578680560943104/image/6117302732849152)


# Code

Let's go over some examples of the causes of the uncaught type error.

## Uncaught TypeError: cannot read property ‘bar’ of null

> Note: `null` has no properties to read or set.

## Uncaught TypeError: cannot set property ‘bar’ of undefined

> Note: `undefined` has no properties to read or set.

## Uncaught TypeError: undefined is not a function

let val = null;
console.log(val());
let num = 20;
console.log(num());

>Note: `undefined` is not a function. Similarly, an object, string, array, etc. is not a function either.

## Uncaught TypeError: cannot use 'in' operator to search for 'x' in 'y'

let val = "Hello from Educative!";
console.log("Hello" in val);

> Note: The `in` operator can only be used to check whether or not ​a property is in an object. 

## Uncaught TypeError: converting circular structure to JSON

let a = { b: "" };
let b = { a: a };
a.b = b;
JSON.stringify(a);

> Note: `a` contains a reference to `b`, and vice versa, which makes variable `a` a circular data structure. `JSON.stringify()` only works with ​cyclic data structures.

For more details, refer to the [official documentation](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/No_properties) on TypeError.

What is an uncaught TypeError in JavaScript?

An uncaught TypeError in JavaScript occurs when an unexpected value is not caught in a try-catch block.

What is an uncaught TypeError in JavaScript?

Code

Uncaught TypeError: cannot read property ‘bar’ of null

Uncaught TypeError: cannot set property ‘bar’ of undefined

Uncaught TypeError: undefined is not a function

Uncaught TypeError: cannot use ‘in’ operator to search for ‘x’ in ‘y’

Uncaught TypeError: converting circular structure to JSON