Get an Object's Key by its Value using JavaScript

Get an Object's Key by its Value in JavaScript #

To get an object's key by it's value:

1. Call the Object.keys() method to get an array of the object's keys.
2. Use the find() method to find the key that corresponds to the value.
3. The find method will return the first key that satisfies the condition.

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function getObjKey(obj, value) {
  return Object.keys(obj).find(key => obj[key] === value);
}

const obj = {country: 'Chile', city: 'Santiago'};

console.log(getObjKey(obj, 'Chile')); // 👉️ "country"

We used the Object.keys method to get an array containing the object's keys.

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const obj = {country: 'Chile', city: 'Santiago'};
console.log(Object.keys(obj)); // 👉️ ['country', 'city']

Then, we called the Array.find method on the keys array.

On each iteration, we use the key to access the object's value and compare it to the supplied value.

If equality check succeeds, the find method returns the corresponding key and short-circuits.

If the equality check never returns true, the find method returns undefined.

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function getObjKey(obj, value) {
  return Object.keys(obj).find(key => obj[key] === value);
}

const obj = {country: 'Chile', city: 'Santiago'};

console.log(getObjKey(obj, 'DoesNotExist')); // 👉️ undefined

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function getObjKey(obj, value) {
  return Object.keys(obj).find(key => obj[key] === value);
}

const obj = {city1: 'Santiago', city2: 'Santiago'};

console.log(getObjKey(obj, 'Santiago')); // 👉️ "city1"

To get multiple object keys that store the same value:

1. Call the Object.keys() method to get an array of the object's keys.
2. Call the Array.filter() method on the array of keys.
3. The filter() method will return a new array containing all the matching keys.

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function getObjKeys(obj, value) {
  return Object.keys(obj).filter(key => obj[key] === value);
}

const obj = {city1: 'Santiago', city2: 'Santiago'};

// 👇️️ ["city1", "city2"]
console.log(getObjKeys(obj, 'Santiago'));

By using the Array.filter method we get an array of all the keys that satisfy the condition.

The function we passed to the filter() method gets called for each key in the array and does not short-circuit on the first truthy response.

Further Reading #

• Get an Object's Value by Index using JavaScript
• How to get a Value of a Map by its Key using JavaScript