How to Set an Object Key by Variable in JavaScript

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Summary: Discover the process of setting an object key dynamically using variables in JavaScript with this comprehensive guide.
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How to Set an Object Key by Variable in JavaScript

When working with JavaScript objects, there are scenarios where you might want to set a key dynamically using a variable. This task can be particularly useful when you're handling dynamic data structures or need to accommodate variable property names. Here's a detailed guide on how to achieve this.

The Traditional Way

Traditionally, when adding a key-value pair to a JavaScript object, you use dot notation or bracket notation. Here’s a recap:

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In both examples, the key names are hard-coded and fixed. But what if the key name is stored in a variable?

Using Variables as Keys

To dynamically set a key name using a variable, you would use bracket notation. Here’s how you can do it:

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In this instance, dynamicKey holds the key name as a string. By using the bracket notation, you can set variableKey in obj to have the value "value".

Dynamic Keys in Function Parameters

Consider a function that takes an object and a key-value pair, and assigns the value to the key dynamically. The function could look something like this:

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This function will add the key-value pair to the object obj based on the key provided.

Using ES6 Computed Property Names

With the advent of ES6, JavaScript introduced computed property names, which make the syntax even cleaner when dealing with dynamic keys. Here’s how you can use them:

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In this example, the value of dynamicKey is directly used to create a property in obj through the use of square brackets within the object literal.

Use Cases

Dynamic Form Handling: Consider a scenario where your application needs to handle form inputs dynamically. By assigning form input names as object keys, you can manage form states efficiently.

API Responses: When dealing with unpredictable API responses, certain responses might include fields that are not predefined in your application. Using variables as keys helps to dynamically accommodate these responses.

Localization: For applications supporting multiple languages, setting object keys based on locale identifiers can be streamlined using this approach.

Conclusion

Setting an object key by variable in JavaScript is essential for situations where you deal with dynamic or unpredictable property names. Whether you're using the classic bracket notation or leveraging ES6 computed property names, this technique will greatly enhance your ability to handle dynamic data structures efficiently. By understanding and implementing these methods, you can write more flexible and maintainable JavaScript code.