Typeerror cannot set properties of undefined

The “typeerror cannot set properties of undefined” is an error message that occurs while working in JavaScript.

We can’t deny the fact that this error is quite frustrating, especially if you don’t know how to resolve it.

Luckily, in this article, we will explore how to resolve this “cannot set properties of undefined” error message.

Apart from that, we’ll also discuss in detail what this error means and why it occurs in your code.

What is “typeerror cannot set properties of undefined”?

The “typeerror: cannot set properties of undefined” error message occurs when you’re trying to set a property on an undefined value.

In a simple words, you are trying to modify a property of a variable that has not been initialized or has not been assigned a value.

For example, if you have an object d and you try to set a property on d[a] without first initializing d[a] as an object or array, you will get this error .

Here’s an example code of how the “TypeError: Cannot set properties of undefined” error can occur with arrays:

let website= [];
website[0].name = 'ITSOURCECODE';

How to fix “typeerror cannot set properties of undefined”?

To fix this error, you’ll have to ensure that the value you’re trying to set a property on is of the expected type (an object or an array) before setting a property on it.

In addition to that, always make sure to initialize your variables before using them.

And check for null or undefined values before accessing properties or assigning values.

Here are the following solutions that will help you resolve this “typeerror: cannot set properties of undefined” error message:

Solution 1: Initialize the variable to an empty object

You just have to initialize the first element of the website array to an object before setting its name property.

let website = [{}];
website[0].name = 'ITSOURCECODE';
console.log(website[0].name);

The first element of website is initialized to an empty object, so we can safely set its name property to ‘ITSOURCECODE’ without getting the “cannot set properties of undefined” error message.

Output:

ITSOURCECODE

Solution 2: Create the variable as an object with the property

This solution creates the variable website as an object with the name property already defined.

By doing so, you can access the name property of the website without encountering the error message.

let website = {
  name: 'ITSOURCECODE'
};
console.log(website.name);

ITSOURCECODE

Solutions 3: Use the nullish coalescing operator

In this case, we use the nullish coalescing operator (??) to assign a default value (”) to the name property of the website if it is undefined or null.

Now, we can safely set the name property of the website.

let website = {};
website.name = 'ITSOURCECODE' ?? '';
console.log(website.name);

Output:

ITSOURCECODE

Conclusion

By executing all the effective solutions for the “typeerror cannot set properties of undefined” that this article has already provided above, it will help you resolve the error.

We are hoping that this article provides you with sufficient solutions.

You could also check out other “typeerror” articles that may help you in the future if you encounter them.

• Typeerror: ‘column’ object is not callable
• Typeerror [clientmissingintents]: valid intents must be provided for the client.
• Typeerror: can’t multiply sequence by non-int of type ‘numpy.float64’

Thank you very much for reading to the end of this article.

Understanding container TypeErrors

Different Python containers have different rules. Lists are ordered and mutable, tuples are ordered and immutable, sets are unordered and hashable-only, dicts are key-value with hashable keys. Confusing them causes TypeError.

Common triggers

• List as dict key. Lists are unhashable — cannot be dict keys or set members.
• Tuple assignment. Tuples are immutable — my_tuple[0] = x raises TypeError.
• Set indexing. Sets have no ordering — my_set[0] is not allowed.
• Dict expects hashable. {[1,2]: "x"} raises TypeError. Use tuple: {(1,2): "x"}.
• Concatenating incompatible types. [1,2] + (3,4) raises TypeError — list + tuple is not allowed.

Diagnostic pattern

# BAD — list as dict key
counts = {}
for word_pair in [("cat","dog"), ("cat","bird")]:
    counts[list(word_pair)] = 1  # TypeError: unhashable type: 'list'

# GOOD — tuple as key
counts = {}
for word_pair in [("cat","dog"), ("cat","bird")]:
    counts[tuple(word_pair)] = 1  # tuples are hashable

Best practices

• Use tuples as dict keys when you need composite keys.
• Use frozenset when you need a set as a dict key.
• Use dataclass with frozen=True for hashable objects.

Caren Bautista

Technical Writer at PIES IT Solution

Responsible for crafting clear, well-structured, and beginner-friendly content across the platform. Handles the writing, proofreading, and editorial review of tutorials, guides, and documentation to ensure every article is accurate, readable, and easy to follow.

Expertise: Technical Writing · Content Creation · Documentation · Editorial Writing · JavaScript · TypeScript · Python · Python Errors · HTTP Errors · MS Excel
 · View all posts by Caren Bautista →