Borislav Hadzhiev
Wed Oct 20 2021·2 min read
Photo by Marc Bombenon
The "toISOString is not a function" error occurs when the toISOString()
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 toISOString()
method on valid date objects.
Here is an example of how the error occurs.
const d = Date.now(); console.log(d); // 👉️ 1639.... // ⛔️ TypeError: toISOString is not a function const result = d.toISOString();
We called the Date.now()
function, which returns an integer and tried to call
the
Date.toISOString()
method on it, which caused the error.
To solve the error, make sure to only call the toISOString()
method on valid
date objects.
// ✅ Works const d1 = new Date().toISOString(); console.log(d1); const d2 = new Date('Sept 24, 22 13:20:18').toISOString(); console.log(d2); // 👉️ 2022-09-24...
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 the "Invalid time value" RangeError.
// ⛔️ RangeError: invalid time value const d1 = new Date('invalid').toISOString(); console.log(d1);
You can console.log
the value you are calling the toISOString
method on and
see if it's a valid Date
object.
You could conditionally check if the value is a Date
object in the following
way.
const d1 = new Date(); if (typeof d1 === 'object' && d1 !== null && 'toISOString' in d1) { const result = d1.toISOString(); console.log(result); }
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 - console.log(typeof null)
, you will get an "object"
value back, so we have to make sure the value is not null
.
toISOString
property.Then we know we can safely call the toISOString
method on the object.