How do I stop returning -0 in Javascript?

Question

I created an event listener with a button that has a code onclick, but sometimes when I click the button over and over again it returns undefined I set it to return random things from an array. Anyways, I found out that since i put my array.length -1 it sometimes returns -0 or undefined instead of just 0 in the console. What would be the best way for me to fix this?

This is my code the button listener is in the main.js file:

HTML

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link rel="stylesheet" href="style.css">
    <title>Document</title>
</head>
<body>
    <div class="root">
        <div>
            <button id="btn1">sleep</button>
        </div>
    </div>

    <script type="module" src="main.js"></script>
</body>
</html>

main.js

import { v1, v2, v3 ,v4 } from './main2.js';


let btn = document.getElementById('btn1');

console.log(v3);
/////////////////////////////////////////////////



btn.addEventListener('click', () => {
    console.log(`${v4[Math.round(Math.random() * v4.length -1
      )]}`)
})

main2.js


let log = {
    One: 'one',
    Two: 'two',
    Three: 'three',
    Four: ['tester1', 'tester2', 'tester3'],
}

export let {One: v1, Two: v2, Three: v3, Four: v4} = log;

Your formula is wrong: `console.log(\`${v4[Math.floor(Math.random() * v4.length)]}\`);` — Treast, Jun 02 '20 at 18:29
I tried that too, but It still returns undefined at a certain point if I keep clicking. — Daniel Gomez, Jun 02 '20 at 18:33
I don't understand? If you're asking if It works when I click on the button, It does I'm just trying to see if there's a way to deter undefined from showing up in the console at all if I were to keep clicking the button over and over. — Daniel Gomez, Jun 02 '20 at 18:43
You sure you’re not setting log or v4 to something else somewhere else? Define them using const not let. — Ibraheem, Jun 02 '20 at 18:51
you're right I just noticed Math.floor() instead of Math.round() — Daniel Gomez, Jun 02 '20 at 18:55
https://stackoverflow.com/questions/7223359/are-0-and-0-the-same — epascarello, Jun 02 '20 at 19:00
https://stackoverflow.com/questions/1527803/generating-random-whole-numbers-in-javascript-in-a-specific-range — epascarello, Jun 02 '20 at 19:01

samanthaj · Accepted Answer · 2020-06-02T19:02:32.927

console.log(`${v4[Math.round(Math.random() * v4.length -1)]}`);

Is choosing an number between -1 and 3

It should be this

console.log(`${v4[Math.random() * v4.length | 0]}`);

Which choses a number between 0 and 3. Math.random() returns a number between 0 and 0.9999999999999999999 so Math.random() * v4.length will return a number between 0 and 3.99999999999999999999

Then | 0 will turn the result into an integer.

| 0 is faster than Math.floor and more idiomatic. See Using bitwise OR 0 to floor a number

How do I stop returning -0 in Javascript?

1 Answers1