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I am trying to do array destructuring in javascript and encounter some very puzzling behavior

Here's the code I have -- 

 let res = {
            start: {},
            end: {},
        };
[res.start.hour, res.start.minute] = [7, 20]
[res.end.hour, res.end.minute] = [17, 30]
console.log(res)

The output is 

{ start: { hour: 17, minute: 30 }, end: {} }

For some reason, [17, 30] were assigned to res.start, instead of res.end.

Furthermore, if I add a console.log statement like below 

 let res = {
            start: {},
            end: {},
        };
[res.start.hour, res.start.minute] = [7, 20]
console.log(JSON.stringify(res));
[res.end.hour, res.end.minute] = [17, 30]
console.log(res)

Then it works. res.end would get the correct value. Output -- 

{"start":{"hour":7,"minute":20},"end":{}}
{ start: { hour: 7, minute: 20 },
  end: { hour: 17, minute: 30 } }

I've searched, and read thru MDN page on destructure, but couldn't find an explanation to this. Appreciate your help in advance.

LandCrawler
  • 17
  • 4

1 Answers1

1

Try this:

let res = {
  start: {},
  end: {}
};
[res.start.hour, res.start.minute] = [7, 20]; // Notice the semicolons.
[res.end.hour, res.end.minute] = [17, 30];
console.log(res);

I copy-pasted your code from the first block into VS Code and used 'Alt + Shift + F' (auto-formatting). It fixed the code to the following, indicating that something is clearly off:

let res = {
  start: {},
  end: {}
};
[res.start.hour, res.start.minute] = [7, 20][(res.end.hour, res.end.minute)] = [
  17,
  30
];
console.log(res);

As it turns out, semicolons do matter sometimes in JavaScript.

J D
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  • 1
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