TypeError: date.getDate is not a function in JavaScript

# TypeError: date.getDate is not a function in JavaScript

The "TypeError: date.getDate is not a function" occurs when the getDate() method is called on a value that is not a date object.

To solve the error, convert the value to a date before calling the method or make sure to only call the getDate() method on valid date objects.

typeerror date getdate is not a function

Here is an example of how the error occurs.

index.js

Copied!
const date = Date.now();
console.log(date); // 👉️ 1639...

// ⛔️ TypeError: date.getDate is not a function
const result = date.getDate();

date getdate is not a function

The Date.now() function returns an integer, so we cannot call the Date.getDate() method on it.

# Only call the `getDate()` method on valid date objects

To solve the error, make sure to only call the getDate() method on valid date objects.

index.js

Copied!
const d1 = new Date().getDate();
console.log(d1); // 👉️ 26

const d2 = new Date('Sept 24, 22 13:20:18').getDate();
console.log(d2); // 👉️ 24

only call getdate method on valid date objects

The code for this article is available on GitHub

You can get a date object by passing a valid date to the Date() constructor.

If an invalid date is passed to the Date() constructor, you will get NaN (not a number) value back.

index.js

Copied!
const d1 = new Date('invalid').getDate();
console.log(d1); // 👉️ NaN

You can console.log the value you are calling the getDate method on and see if it's a valid Date object.

# Check if the value is a `Date` object before calling `getDate()`

You could conditionally check if the value is a Date object in the following way.

index.js

Copied!
const d1 = new Date();

if (typeof d1 === 'object' && d1 !== null && 'getDate' in d1) {
  const result = d1.getDate();
  console.log(result); // 👉️ 16
}

check if value is date object before calling getdate

The code for this article is available on GitHub

Our if condition uses the logical AND (&&) operator, so for the if block to run, all of the conditions have to be met.

We first check if the d1 variable stores a value with a type of object because dates have a type of object.

Then we check if the variable is not equal to null. Unfortunately, if you check the type of null with console.log(typeof null), you will get an "object" value back, so we have to make sure the value is not null.

The last thing we check for is that the object contains the getDate property.

Then we know we can safely call the getDate() method on the object.

This approach is called duck-typing.

When using duck-typing, we simply check if the object implements specific properties or methods and if it does, we assume it's an object of the correct type.

I wrote a book in which I share everything I know about how to become a better, more efficient programmer.

You can use the search field on my Home Page to filter through all of my articles.

TypeError: date.getDate is not a function in JavaScript