Does the array.sort() method behave in-place when used on Object.keys()?

When utilizing the .sort() method of JavaScript arrays, the array is altered directly and a reference to the array is returned.

Object.keys(obj) generates an array with all the keys from object obj.

It's important to note that in JavaScript, object keys are not guaranteed to be in a specific order according to standards.

This brings up an interesting conflict between the two "rules": "array.sort() is in-place" vs "Object keys are not ordered".

So what exactly happens when we execute Object.keys(obj).sort()?

  • Do the keys of the object get sorted in place and remain sorted if the object isn't modified?
  • Is a temporary unspecified copy of the array of object keys created and then sorted?
  • Or does something else occur?

Is this behavior explicitly outlined in the standard or does it differ based on implementation?

javascriptarrayssortingjavascript-objectsin-place

Answer №1

The correct answer is the second option: An ephemeral anonymous duplicate of the array of object keys is generated and organized.

According to the ECMA specifications, it is specified that the output of Object.keys should be a fresh array instance each time. This implies that the resulting array does not hold the original keys of the object, unlike Java's keySet; instead, it is merely a replica.

Answer №2

JavaScript objects do not follow a specific order. While you can rearrange the keys of an object into an array, sorting the actual object is not possible.

var example = {'x': 45, 'y': 72, 'z': 31};
console.log(Object.keys(example).sort());
// yields: ["x", "y", "z"]
// however, example retains its original order: Object {x: 45, y: 72, z: 31}

Object.keys(example).sort() generates an ordered array of "x", "y", and "z", but the object itself remains unordered (depending on the browser's implementation).

To elaborate, when you execute Object.keys(example).sort(), a temporary sorted copy of the object keys is produced while leaving the original object untouched.

Answer №3

Chances are, JS will generate a temporary unidentified duplicate of the array of objects and then proceed to arrange it.

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