Is there a way to ensure javascript object properties are ordered in a specific way?

Question

I have a JavaScript object that looks like this:

Const data = {
x: 1,
y: 2,
z: 3
a: 4,
b: 5,
c: 6
};

We have a signing service in our Angular 6 application which stringifies this object, hashes the string, then attached a signature to it. Then it saves it to a firestore database. The database likes to order the properties alphabetically so it ends up looking like this:

{
a: 4,
b: 5,
c: 6,
x: 1,
y: 2,
z: 3
}

When we retrieve this object from the database and try to validate the signature, it fails. It fails because when you stringify this object, the alphabetical order of the properties results in a different string compared to when we signed it. This results in a different hash which doesn’t match with the original signature.

Our current solution to this problem is that we write out the order of the properties alphabetically in the code, but we’d like to make this fool proof (ex. If another developer comes along and adds a property to the bottom, say d, not realizing it’s supposed to be alphabetical). I’m told by a colleague that there is some way of telling Javascript to order the properties according to its own algorithm. If we could do that, then we’d order the properties according to that algorithm before stringifying, hashing, and signing, and then when we retrieve the object from the database, do the same thing: order the properties according to Javascript’s algorithm, stringify, hash, and validate.

Does anyone know what this Javascript ordering is and how to do it?

Usually I turn it into an array of key : value objects, then I order it by values — Mosè Raguzzini
– Mosè Raguzzini, Commented Feb 6, 2019 at 16:58

Sam · Accepted Answer · 2019-02-06 17:34:58Z

1

There isn't a way for JS to naturally order an object, you're going to have to tinker with it yourself.

The easiest way that I can think of to do this would be to use an array and sort from there.

This will return you the following array...

Object.entries(test).sort((a, b) => a[1] - b[1])

returns

[ [ 'x', 1 ],
  [ 'y', 2 ],
  [ 'z', 3 ],
  [ 'a', 4 ],
  [ 'b', 5 ],
  [ 'c', 6 ] ]

If you want it back in an object,

Object.assign({}, ...Object.entries(test).sort((a, b) => a[1] - b[1]).map(([key, value]) => ({[key]: value})) )

returns

{ x: 1, y: 2, z: 3, a: 4, b: 5, c: 6 }

answered Feb 6, 2019 at 17:34

Sam

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1 Comment

Gibran Shah Over a year ago

Thanks, I'll suggest this as a possible solution.

kemicofa · Accepted Answer · 2019-02-06 16:59:33Z

1

Create a custom stringify function that handles putting the object in the correct order.

const data = {
 a: 4,
 b: 5,
 c: 6,
 x: 1,
 y: 2,
 z: 3
}

function customStringify(d){
  return '{'+Object
  .entries(d)
  .sort(([,v1],[,v2])=>v1-v2)
  .map(([k,v])=>`${k}:${v}`)
  .join(",")+'}';
}

const res = customStringify(data);

console.log(res);

answered Feb 6, 2019 at 16:59

kemicofa

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1 Comment

Gibran Shah Over a year ago

Thanks, I'll suggest this as a possible solution.

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