Unique Values

In general, Faker methods do not return unique values.

faker.seed(55);
faker.animal.type(); //'cat'
faker.animal.type(); //'bird'
faker.animal.type(); //'horse'
faker.animal.type(); //'horse'

Some methods and locales use much smaller data sets than others. For example, faker.animal.type has only 13 possible animals to choose from. In contrast, faker.person.fullName() pulls from a list of hundreds of first names, surnames, and prefixes/suffixes, so it can generate hundreds of thousands of unique names. Even then, the birthday paradox means that duplicate values will quickly be generated.

Sometimes, you want to generate unique values. For example, you may wish to have unique values in a database email column.
There are a few possible strategies for this:

1. Use faker.helpers.uniqueArray() if you want to generate all the values at one time. For example:

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

2. If there are insufficient values for your needs, consider prefixing or suffixing values with your own sequential values, for example you could prefix 1., 2. to each generated email in turn.

3. Build your own logic to keep track of a set of previously generated values and regenerate values as necessary if a duplicate is generated

4. Use a third party package to enforce uniqueness such as enforce-unique

Note you can supply a maximum time (in milliseconds) or maximum number of retries.

import { EnforceUniqueError, UniqueEnforcer } from 'enforce-unique';

const uniqueEnforcerEmail = new UniqueEnforcer();

function createRandomUser() {
  const firstName = faker.person.firstName();
  const lastName = faker.person.lastName();
  const email = uniqueEnforcerEmail.enforce(
    () =>
      faker.internet.email({
        firstName,
        lastName,
      }),
    {
      maxTime: 50,
      maxRetries: 50,
    }
  );

  return {
    firstName,
    lastName,
    email,
  };
}