---
title: Greatest common divisor
id: 5a23c84252665b21eecc7e82
challengeType: 5
---

## Description
<section id='description'>
Write a function that returns the greatest common divisor of two integers.
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>gcd</code> should be a function.
    testString: assert(typeof gcd=='function','<code>gcd</code> should be a function.');
  - text: <code>gcd(24,36)</code> should return a number.
    testString: assert(typeof gcd(24,36)=='number','<code>gcd(24,36)</code> should return a number.');
  - text: <code>gcd(24,36)</code> should return <code>12</code>.
    testString: assert.equal(gcd(24,36),12,'<code>gcd(24,36)</code> should return <code>12</code>.');
  - text: <code>gcd(30,48)</code> should return <code>6</code>.
    testString: assert.equal(gcd(30,48),6,'<code>gcd(30,48)</code> should return <code>6</code>.');
  - text: <code>gcd(10,15)</code> should return <code>5</code>.
    testString: assert.equal(gcd(10,15),5,'<code>gcd(10,15)</code> should return <code>5</code>.');
  - text: <code>gcd(100,25)</code> should return <code>25</code>.
    testString: assert.equal(gcd(100,25),25,'<code>gcd(100,25)</code> should return <code>25</code>.');
  - text: <code>gcd(13,250)</code> should return <code>1</code>.
    testString: assert.equal(gcd(13,250),1,'<code>gcd(13,250)</code> should return <code>1</code>.');
  - text: <code>gcd(1300,250)</code> should return <code>50</code>.
    testString: assert.equal(gcd(1300,250),50,'<code>gcd(1300,250)</code> should return <code>50</code>.');

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='js-seed'>

```js
function gcd(a, b) {
  // Good luck!
}
```

</div>



</section>

## Solution
<section id='solution'>


```js
function gcd(a, b) {
  return b==0 ? Math.abs(a):gcd(b, a % b);
}

```

</section>