How to Destructure an Object into Existing Variables in JavaScript

Have you ever encountered the need to destructure an object into existing variables in JavaScript? If so, you might have faced a challenge when trying to incorporate this into an if block while keeping the variables accessible outside of that block. In this blog post, I will guide you through the process of achieving this.

Let’s start with the scenario where you have a function that returns an object:

const doSomething = () => {
 return { a: 1, b: 2 }
}

const { a, b } = doSomething()

Now, you want to wrap this code inside an if block to execute it only when a certain condition, represented by /* my conditional */, is met. To make the variables a and b accessible outside of the block, you need to declare them beforehand as undefined variables and update their values when the data is available.

Here’s how you can accomplish this:

let a, b

const doSomething = () => {
 return { a: 1, b: 2 }
}

if (/* my conditional */) {
 ({ a, b } = doSomething())
}

One thing to note is that in order to remove the const before the object destructuring, you need to wrap the entire line in parentheses. Additionally, if you prefer not to use semicolons, you should add a semicolon before the line to avoid any potential issues with parentheses. This is similar to how you would handle an IIFE (immediately-invoked function expression) to prevent confusion in the code:

1
2
3

;(() => {
 //...
})()

By following these steps, you can effectively destructure an object into existing variables while working within an if block and ensure the variables remain accessible outside of that block.

Tags: JavaScript, object destructuring, variable assignment, coding techniques