Unique Values

Generally speaking, DataFaker methods do not return unique values. However, some methods and locales use significantly smaller datasets than others. For instance, faker.animal.type has only 44 possible animal types to choose from. In contrast, faker.person.fullName() draws from lists of hundreds of first names, last names, and prefixes/suffixes, allowing it to generate hundreds of thousands of unique names. Even so, the birthday paradox means that duplicate values will be generated before long.

Therefore, there are times when you may want to generate unique values. For example, you might want unique values in a database email column. There are several possible strategies to achieve this:

1. If you want to generate all values at once, use faker.helpers.uniqueArray(). For example:

faker.helpers.uniqueArray(faker.internet.email, 1000); // will generate 1000 unique email addresses

2. If the available values are insufficient for your needs, consider using your own sequential values as a prefix or suffix. For example, you can sequentially add 1., 2., etc., to the prefix of each generated email.
3. Build your own logic to keep track of a set of previously generated values, and regenerate values as needed when duplicates are produced.
4. Use third-party packages to enforce uniqueness, such as enforce-unique or @dpaskhin/unique.