Find a Value's Key in a JavaScript Object

I don’t know how many times I have accessed a JavaScript object’s value by its key or how I could arrive at a reasonable guess. What I do know is the number of times that I found the key from its corresponding value: once. This StackOverflow post is probably where you will end up if you search for how to accomplish this. The solution that I used and a variable version from another solution on the same post are copied below for reference.

// As a function
function getKeyByValue(object, value) {
	return Object.keys(object).find((key) => object[key] === value);
}

// As a variable
const key = Object.keys(object).find((key) => object[key] === value);

Using the code without modifications worked flawlessly in my project, but for some reason it was difficult for me to understand exactly what the code did. Perhaps my confusion was from the multiple uses of “object” and “key” along with “Object” (capital O) and “keys” (plural). No matter the cause, breaking down the code and looking at the result of each step cleared up my confusion. This is what that process looked like.

The Process

The first step is defining an object with some amount of data in it.

const movies = {
	Inception: "Christopher Nolan",
	Jaws: "Steven Spielberg",
	Watchmen: "Zack Snyder",
};

Next, Object.keys() is used to create an array of the object’s keys.

const arrayOfKeys = Object.keys(movies);
console.log(arrayOfKeys);

// Logs to the console: ["Inception", "Jaws", "Watchmen"]

Now that the keys are separated from their values and stored in an array, the Array.find() method is used to determine which key corresponds to our specified value. I updated the variable version of the code to be more specific to this example. Finding the movie that Steven Spielberg directed in the movies object looks like this.

const correspondingKey = arrayOfKeys.find((title) => movies[title] === "Steven Spielberg");

console.log(correspondingKey);
// Logs to the console: "Jaws"

Thinking through each iteration of the keys can also be helpful. The first key in the array is “Inception.” Does movies[Inception] === "Steven Spielberg"? No. The value of movies[Inception] is “Christopher Nolan.” The second key in the array is “Jaws.” Does movies[Jaws] === "Steven Spielberg"? Yes.