TypeError: toLocaleDateString is not a function in JS [Fix]

# TypeError: toLocaleDateString is not a function in JS

The "TypeError: toLocaleDateString is not a function" occurs when the toLocaleDateString() 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 toLocaleDateString method on valid dates.

Here is an example of how the error occurs.

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const d = Date.now();
console.log(d); // 👉️ 1639....

// ⛔️ TypeError: toLocaleDateString is not a function
const result = d.toLocaleDateString('en-US');

We called the Date.now() function, which returns an integer and tried to call the Date.toLocaleDateString() method on it, which caused the error.

# Only call the toLocaleDateString method on valid Date objects

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

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const d1 = new Date().toLocaleDateString('en-US');
console.log(d1);

const d2 = new Date('Sept 24, 22 13:20:18').toLocaleDateString('en-US');
console.log(d2); // 👉️ 9/24/2022

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

Note that if an invalid date is passed to the Date() constructor, you would get "Invalid date" back.

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const d1 = new Date('invalid').toLocaleDateString('en-US');
console.log(d1); // 👉️ "Invalid Date"

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

# Check if the value is a valid Date before calling toLocaleDateString

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

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const d1 = new Date();

if (typeof d1 === 'object' && d1 !== null && 'toLocaleDateString' in d1) {
  const result = d1.toLocaleDateString('en-US');
  console.log(result); // 👉️ 12/16/...
}

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

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

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console.log(typeof null); // 👉️ object

Then we know we can safely call the toLocaleDateString method on the object.