Why value from variable "y" is 5? not 7?

user_11241731 0
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first of all sorry for my bad english

so, this is my code:

let x = 5
const {x: y=7} = {x}

console.log(y) // output is 5

but why 5? is not 7?

destructuring object javascript
2 Answers

{x} is shorthand for {x: x}. Since the value of x is 5, this is equivalent to {x: 5}.

That means your code is equivalent to

const {x: y=7} = {x: 5}

This sets y to the value of the x property in {x: 5}. If there were no property, it would use the default value of 7; but since the property does exist, its value is used, so it sets y to 5.

Compare with

let a = 5;
const {x: y=7} = {a}

This will set y to 7 because there's no x property in the object.

user_14918950

note : equals assignment have a left to right operation in other words... the left side takes greater precedence over the right and overrides the any value on the left

const{ x = y } = {x = 5}
x........ maps to..........x
y......... maps to..........5 (overriding the previous y value)

Also........... You can take it this way

what you simply wrote was

y=7
y=5

y=5 came last so it replaced the previous value

user_108238430
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