Set a custom start and end range in an array that displays a random string?

Question

I am playing around with JavaScript while preparing for my junior developer interview.

I am trying to write a function that accepts two parameters, a beginning point and an ending point, in an array. This function should generate a random name within a custom start and end point of the array. I seemed close to getting it right, but it displays NaN. What is NaN?

Here is the code I wrote.

const names = ['Kitana', 'Liu Kang', 'Sonya Blade', 'Johnny Cage', 'Jax Briggs', 'Smoke', 'Sheeva', 'Jade']

const section = document.querySelector('section')

const para = document.createElement('p');

// Add your code here
function random(beginIndex, endIndex) {
  for (let beginIndex = 0; beginIndex < names.length; beginIndex = beginIndex + endIndex) {

    let newRangeOfIndices = names[beginIndex]

    const randomName = Math.floor(Math.random() * newRangeOfIndices)

    para.textContent = randomName
  }
}

random(2, 5)

// Don't edit the code below here!

section.innerHTML = ' ';

section.appendChild(para);

<section></section>

You will notice that I already set a custom limit in the function to be run, 2 to 5. But it's still not working. Please help me out.

Does this answer your question? [Getting a random value from a JavaScript array](https://stackoverflow.com/questions/4550505/getting-a-random-value-from-a-javascript-array) — pilchard, Aug 28 '22 at 09:17
and [Generating random whole numbers in JavaScript in a specific range](https://stackoverflow.com/questions/1527803/generating-random-whole-numbers-in-javascript-in-a-specific-range) — pilchard, Aug 28 '22 at 09:17

score 2 · Accepted Answer · answered Aug 28 '22 at 09:15

You don't for loop to get a random number.

To get a random index.

let randomIndex = Math.floor(Math.random() * (endIndex - beginIndex + 1) + beginIndex)

Then get the random name from the names array.

let randomName = names[randomIndex]

const names = ['Kitana', 'Liu Kang', 'Sonya Blade', 'Johnny Cage', 'Jax Briggs', 'Smoke', 'Sheeva', 'Jade']

const section = document.querySelector('section')

const para = document.createElement('p');

// Add your code here
function random(beginIndex, endIndex) {
    let randomIndex = Math.floor(Math.random() * (endIndex - beginIndex + 1) + beginIndex)  
    let randomName = names[randomIndex]

    para.textContent = randomName
}

random(2, 5)

// Don't edit the code below here!

section.innerHTML = ' ';

section.appendChild(para);

<section></section>

Md. Jamal Uddin · Answer 2 · 2022-08-28T10:17:27.537

The author asked two questions here... the first one related to the code and here is my solution:

const names = ['Kitana', 'Liu Kang', 'Sonya Blade', 'Johnny Cage', 'Jax Briggs', 'Smoke', 'Sheeva', 'Jade'];

// create a generic randomName function that takes 3 parameters beginIndex, endIndex and an array which returns a random positioned value within the range
function randomName(beginIndex, endIndex, arr) {
  const randomNumber = Math.floor(Math.random() * (endIndex - beginIndex + 1) + beginIndex);
    return arr[randomNumber];
}

// call the function with the proper argument
randomName(2, 5, names);

the second question is What is NaN?

Answer: as stated by MDN Docs

The global NaN property is a value representing Not-A-Number.

When calculating numbers but sending a string value to parse, the JavaScript parser is throwing an error that it is Not-A-Number.

let's see we have two variables

let x = 10;
let y = 'hello';
    
console.log(typeof x); // number
console.log(typeof y); // string

// try to multiplied x by y
console.log(x * y);    // NaN

In Your case:

function random(beginIndex, endIndex) {
  for (let beginIndex = 0; beginIndex < names.length; beginIndex = beginIndex + endIndex) {

    // this will be a string that extracts the value of the beginIndex position value from the names array.
    let newRangeOfIndices = names[beginIndex]

    // here you try to multiply the Random Number by a string and getting NaN
    const randomName = Math.floor(Math.random() * newRangeOfIndices)

    para.textContent = randomName
  }
}

random(2, 5)

Best wishes for your interview

I think I probably got a bit of some lecture here. – Matrion Aug 29 '22 at 07:37 — Matrion, Aug 29 '22 at 07:37
Glad to know that you understood – Md. Jamal Uddin Aug 30 '22 at 08:25 — Md. Jamal Uddin, Aug 30 '22 at 08:25

score 0 · Answer 3 · answered Aug 28 '22 at 09:19

0

Use:

return Math.random() * (max - min) + min;

To get a number as min-max. Then, use the random number output as an index in the array. Always avoid for loops in situations like this - there is most likely always another way to do it.

answered Aug 28 '22 at 09:19

Nebula Developments

11
1

score 0 · Answer 4 · answered Aug 28 '22 at 09:41

0

Math.floor(Math.random()* (max_number)+min_number)

you are using string not index number. newRangeOfIndices is giving the value of particular index. this will work.

answered Aug 28 '22 at 09:41

Rishabh Patidar

1
1

Set a custom start and end range in an array that displays a random string?

4 Answers4