Generate an array with random data without using a for loop

Question

I am using the faker.js library to generate random data and I have a couple of factory functions that generate a series of user data:

const createUser = () => {
  return {
    name: faker.name.findName(),
    email: faker.internet.email(),
    address: faker.address.streetAddress(),
    bio: faker.lorem.sentence(),
    image: faker.image.avatar(),
  };
};

const createUsers = (numUsers = 5) => {
  return Array(numUsers).fill(createUser());
};

let fakeUsers = createUsers(5);
console.log(fakeUsers);

The problem with this Array.fill approach is that it returns the same data n number of times. I want 5 different users to be returned from my factory.

How do I do this?

no reason - just want to know alternate ways of doing things with Array.fill — Amit Erandole
– Amit Erandole, Commented Mar 17, 2017 at 15:45
Set aside the Array functors there are tons of other ways to loop in JS. You may even do this job recursively. — Redu
– Redu, Commented Mar 17, 2017 at 15:59

le_m · Accepted Answer · 2017-03-17 16:54:47Z

33

Array.from allows you to create an array and initialize it with values returned from a callback function in one step:

const createUsers = (numUsers = 5) => {
    return Array.from({length: numUsers}, createUser);
}

answered Mar 17, 2017 at 16:54

le_m

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1 Comment

Machado Over a year ago

No empty fills, no maps, just exactly what should be done. Thanks!

Aron · Accepted Answer · 2017-03-17 15:47:30Z

7

Create an array with blanks, and then use .map() to create users:

const createUsers = (numUsers = 5) => {
    return Array(numUsers)
        .fill(null)
        .map(createUser);
}

answered Mar 17, 2017 at 15:47

Aron

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Comments

enthe0s · Accepted Answer · 2023-11-03 13:42:31Z

5

You can now do this with the multiple helper much more easily as of the latest version (v8.0.0):

const createUser = () => {
  return {
    name: faker.person.fullName(),
    email: faker.internet.email(),
    address: faker.location.streetAddress(),
    bio: faker.lorem.sentence(),
    image: faker.image.avatar(),
  };
};

faker.helpers.multiple(createUser, { count: 5 })

See the docs for more info: https://fakerjs.dev/api/helpers.html#multiple

edited Nov 3, 2023 at 13:42

answered May 16, 2023 at 17:58

enthe0s

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1 Comment

aland Over a year ago

name and address are deprecated, use person and location respectively.. instead of name.findName() use person.fullName() instead of address.streetAddress() use location.streetAddress()

Gorka Hernandez · Accepted Answer · 2017-03-17 15:57:43Z

4

Creating an array via the Array constructor will yield an non mappable (or iterable for that matter) array.

This happens because the constructor will give you an array with X uninitialized values, causing map to fail. Using fill to initialize the values, even if initialized to null or undefined, will work:

const createUser = () => {
  return {
    name: faker.name.findName(),
    email: faker.internet.email(),
    address: faker.address.streetAddress(),
    bio: faker.lorem.sentence(),
    image: faker.image.avatar()
  }
}

const createUsers = (numUsers = 5) => {
  return new Array(numUsers)
    .fill(undefined)
    .map(createUser);
}

let fakeUsers = createUsers(5)
console.log(fakeUsers)

https://jsbin.com/punesorico/edit?html,js,console

answered Mar 17, 2017 at 15:57

Gorka Hernandez

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1 Comment

Amit Erandole Over a year ago

nice explanation

Redu · Accepted Answer · 2017-03-17 16:16:01Z

1

Here is another way of doing this job by a TCO recursive function;

function getFakeObject(){
  return Array(5).fill()
                 .reduce(o => Object.assign(o,{[String.fromCharCode(...Array(5).fill().map(_ => ~~(Math.random()*26)+65))] : String.fromCharCode(...Array(5).fill().map(_ => ~~(Math.random()*26)+97))}),{});
}

function makeFakeObjectsArray(n, r = []){
 return n ? makeFakeObjectsArray(n-1,(r.push(getFakeObject()),r)) : r;
}

console.log(makeFakeObjectsArray(5));

answered Mar 17, 2017 at 16:16

Redu

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