September 16, 2022

How to Get a Random Property of an Object in JavaScript

Justin Golden

The Function

This one is short and sweet:

const randomProperty = (obj) => {
  const keys = Object.keys(obj);
  return obj[keys[(keys.length * Math.random()) << 0]];
};

The Explanation

const keys = Object.keys(obj);

We get all possible keys using Object.keys(). This alias cleans up the second line and ensures we don’t need to run Object.keys() twice.

return obj[keys[(keys.length * Math.random()) << 0]];

We return obj[keys[RANDOM_KEY_NUMBER]] where RANDOM_KEY_NUMBER is a random number between zero and the number of keys minus one.

If we have four keys, they would have indicies 0,1,2,3 and keys.length would be 4.

Math.random() generates a random float between 0 and 1. Multiplied by keys.length, this gets us a number between zero and the number of keys. But we want a number between zero and the number of keys minus one. In our example, 4 is the number of keys, but that’s not a valid index. We use a left bit shift << on zero to effectively round down to the nearest integer. So 3.45 would become 3, which is a valid index.

Usage

Use this function for getting a random option from a list, for example, a random user, location, or color.

You can also call it by just passing an array in directly, for example: randomProperty(['apple', 'orange', 'banana']).