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, Mar 17 '17 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, Mar 17 '17 at 15:59

score 8 · Accepted Answer · answered Mar 17 '17 at 16:54

8

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 '17 at 16:54

le_m

15,910
7
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65

No empty fills, no maps, just exactly what should be done. Thanks! – Machado Oct 17 '19 at 16:30

score 6 · Answer 2 · answered Mar 17 '17 at 15:47

6

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 '17 at 15:47

Aron

6,128
4
24
46

score 3 · Answer 3 · answered Mar 17 '17 at 15:57

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

score 1 · Answer 4 · answered Mar 17 '17 at 16:16

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));

Generate an array with random data without using a for loop

4 Answers4

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