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How to Get a Key in a JavaScript Object by its Value?

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Sometimes, we may want to get the key of a JavaScript object by its value.

In this article, we’ll look at how to get a key in a JavaScript object by its value.

Object.keys and Array.prototype.find

We can use the Object.keys method to return an array of non-inherited string keys in an object.

And we can use the JavaScript array’s find method to return the first instance of something that meets the given condition in an array.

For instance, we can write:

const object = {
  a: 1,
  b: 2,
  c: 3
}
const value = 2;
const key = Object.keys(object).find(key => object[key] === value);
console.log(key)

We have the object object that we want to search for the key in.

And value is the value of the key that we want to search for.

We get all the keys of object with Object.kets .

Then we call find with a callback that returns object[key] === value .

key is the object key being iterated through to find the key name for the given value .

Therefore, we should see that key is 'b' from the console log.

Object.keys and Array.prototype.filter

We can replace the find with filter and destructure the result from the array returned by filter .

For instance, we can write:

const object = {
  a: 1,
  b: 2,
  c: 3
}
const value = 2;
const [key] = Object.keys(object).filter(key => object[key] === value);
console.log(key)

And we get the same result for key as in the previous example.

Object.entries and Array.prototype.find

We can use the Object.entries method to return an array of arrays of key-value pairs of an object.

Therefore, we can use the returned array to find the key of the object with the given value.

For instance, we can write:

const object = {
  a: 1,
  b: 2,
  c: 3
}
const value = 2;
const [key] = Object.entries(object).find(([, val]) => val === value);
console.log(key)

We call find with a callback that has the parameter with the val variable destrutured from the parameter.

val has the value of the in the key-value pair array.

So when we return val === value , we return the same boolean expression as the first example.

From the returned result of find , we can get the key of from the returned key-value pair by destructuring it.

And so we get the same value of key logged in the console log.

Conclusion

We can find a key that has the given value by using native JavaScript object methods.

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