Today I Learned

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Destructure into an existing array

This one’s got my head spinning. Let’s say you have an existing array:

const fruits = ['banana', 'apple', 'kumquat']

You can destructure right into this array.

{name: fruits[fruits.length]} = {name: 'cherry'}

//fruits is now ['banana', 'apple', 'kumquat', 'cherry']

Generally, I would think of the {name: <some var id>} = ... syntax as renaming the value that you are destructuring, but now I think of it more as defining a location that the value will be destrcutured to.

If you try to declare a new variable in the same destructuring however you will get an error if you use const:

const {name: fruits[fruits.length], color} = {name: 'cherry', color: 'red'}
// Uncaught SyntaxError: Identifier 'fruits' has already been declared

Or the new variable will go onto the global or window object if you don’t use const:

{name: fruits[fruits.length], color} = {name: 'cherry', color: 'red'}
// 'red'
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