Solving the value.isUTC is not a function Error in React Hook Form with DatePicker and Moment.js

Solving the value.isUTC is not a function Error in React Hook Form with DatePicker and Moment.js

When encountering the error value.isUTC is not a function in a React component using the DatePicker from Material-UI with moment dates, it usually indicates a mismatch between the expected data type by the component and the actual data type of the date value provided. This blog post will guide you through understanding the error and how to resolve it effectively.

Understanding the Error

The error message TypeError: value.isUTC is not a function suggests that the DatePicker component expects a date object with a isUTC method. This method is typically part of the Moment.js library, used to check whether the date is in UTC format. However, the error arises because the provided date object does not have this method, likely because it's either not a Moment object or it's a JavaScript Date object.

The Cause

In the code snippet provided, the DatePicker component is configured to use a Moment.js object for its value, as indicated by the conversion moment(field.value). However, the onChange handler converts the selected date back to a JavaScript Date object with date.toDate(). This can lead to inconsistencies, especially if other parts of your application or the DatePicker itself expect a Moment.js object.

The Solution

To resolve this issue, ensure consistency in the date object types used throughout the DatePicker component. If your application relies on Moment.js objects, you should maintain this format without converting back and forth between Moment.js and JavaScript Date objects.

Here's an updated version of the component that maintains the use of Moment.js objects:

  render={({ field }) => (
      label="Start Date"
      value={field.value ? moment(field.value) : null}
      renderInput={(params) => <TextField {...params} />}
      onChange={(date) => {
        // Keep the date as a Moment object

In this revised code, the onChange handler directly passes the Moment.js date object to field.onChange, avoiding the conversion to a JavaScript Date object. This ensures that the DatePicker component and any other parts of your application expecting a Moment.js object receive the correct type.

Best Practices

  • Consistency in Date Types: Choose a single date type (Moment.js or JavaScript Date) and use it consistently across your application to prevent type mismatches.
  • Understand Library Requirements: Ensure you understand the data types expected by third-party libraries or components you're using, such as Material-UI's DatePicker.
  • Error Handling: Implement error handling for your input components to catch and manage type mismatches or invalid values gracefully.


The TypeError: value.isUTC is not a function error is a common issue that arises from a mismatch in expected data types within React components using date libraries. By ensuring consistency in the use of date object types and understanding the requirements of the libraries you're working with, you can avoid such errors and create more robust applications.