Extracting common methods

In this section, we’ll pull out the validation clauses that are duplicated in the addNew and replace functions, moving them into a shared validate function.

Let’s start now with the validate function:

1. Below the definitions of addNew and replace, add the following function named validate. This contains the two guard clauses that appeared in each of the original functions. As a simplification, the item argument has been destructured into name and dob arguments:

   const validate = ({ name, dob }) => {
     if (empty(name)) {
       return { error: 'Please provide a name.' };
     }
     if (invalidDob(dob)) {
       return {
         error:
           'Please provide a date of birth in the YYYY-
             MM-DD format.'
       };
   &...