Get a Random Property from an Object in JavaScript

Get a Random Property from an Object #

To get a random property from an object:

1. Call the Object.keys() method to get an array of the object's keys.
2. Use the Math.floor() and Math.random() functions to get a random index of the array.
3. Use the random index to access one of the object's properties.

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const obj = {
  name: 'Tom',
  country: 'Chile',
  age: 30,
};

function getRandomProperty(obj) {
  const keys = Object.keys(obj);

  return keys[Math.floor(Math.random() * keys.length)];
}

console.log(getRandomProperty(obj)); // 👉️ name
console.log(getRandomProperty(obj)); // 👉️ age
console.log(getRandomProperty(obj)); // 👉️ name

We created a reusable function that returns a random property from an object.

The first step is to get the an array of the object's keys using the Object.keys method.

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const obj = {
  name: 'Tom',
  country: 'Chile',
  age: 30,
};

// 👇️ ['name', 'country', 'age']
console.log(Object.keys(obj));

The Math.floor function, rounds a number down if the number has a decimal, otherwise it returns the number as is.

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console.log(Math.floor(2.99)); // 👉️ 2
console.log(Math.floor(2.01)); // 👉️ 2
console.log(Math.floor(2)); // 👉️ 2

The Math.random function returns a random number in the range 0 to less than 1. The function could return 0, but it could never return 1.

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console.log(Math.random()); // 👉️ 0.1034543...
console.log(Math.random()); // 👉️ 0.5438454...
console.log(Math.random()); // 👉️ 0.5438483...

// 👇️ Multiplied by keys.length
const keys = ['name', 'country', 'age'];

console.log(Math.random() * keys.length); // 👉️ 2.534...
console.log(Math.random() * keys.length); // 👉️ 1.543...
console.log(Math.random() * keys.length); // 👉️ 1.754...
console.log(Math.random() * keys.length); // 👉️ 0.324...

The max value we could get is, if Math.random returns 0.999... and we multiply it by the array's length (3). We would get back a value of 2.997.

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console.log(0.999 * 3); // 👉️ 2.997

However, because indexes are zero-based in JavaScript, the last element in the array has an index of array.length - 1. For this reason, we used the Math.floor() function to round the number down to the next integer, which is 2 (the last index in the array of keys).

Conversely, the min value we could get is, if Math.random() returns 0. In this case, we would multiply 0 by the array's length and get 0 back.

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console.log(0 * 3); // 👉️ 0

Calling the Math.floor function with 0 returns the number as is. In this scenario, we would access the first element in the keys array.

The expression returns an index from 0 up to (but not including) array.length. This guarantees us that we could never access an index of out bounds.

Here's the complete code snippet.

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const obj = {
  name: 'Tom',
  country: 'Chile',
  age: 30,
};

// 👇️ ['name', 'country', 'age']
console.log(Object.keys(obj));

function getRandomProperty(obj) {
  const keys = Object.keys(obj);

  return keys[Math.floor(Math.random() * keys.length)];
}

console.log(getRandomProperty(obj)); // 👉️ country
console.log(getRandomProperty(obj)); // 👉️ age
console.log(getRandomProperty(obj)); // 👉️ country

Further Reading #

• How to get a Random Float in a Range using JavaScript
• Get Multiple Random Elements from an Array in JavaScript