Javascript sort object key indexes

Question

here is my structure/example:

let arrWeekdays = ['Montag', 'Dienstag', 'Mittwoch', 'Donnerstag', 'Freitag', 'Samstag'];

let obj1 = {
 'Montag' : ['test string'],
 'Dienstag' : ['test string'],
 'Mittwoch' : ['test string'],
 'Donnerstag' : ['test string'],
 'Freitag' : ['test string'],
 'Samstag' : ['test string']
}

let obj2 = {
 'Donnerstag' : ['test string'],
 'Samstag' : ['test string'],
 'Montag' : ['test string'],
 'Dienstag' : ['test string'],
 'Mittwoch' : ['test string'],
 'Freitag' : ['test string']
}


for ( key in objWeekdays ) {
  // do something
}

"objectWeekdays" in for in loop is sometimes ordered object as "obj1", but sometimes also unordered as "obj2".

My problem:

for in with obj1 => key index of "Montag" is 0

for in with obj2 => key index of "Montag" is 2

Is there any way to sort Object keys before "for in" loop?

I would like always to start with "Montag" in for in loop.

Thanks in advance for any advice or help.javascri

just because im curious: why would you need the attributes to be in order? — SpaceNinjaApe, Feb 17 '21 at 10:14

score 2 · Answer 1 · answered Feb 17 '21 at 10:00

2

You could iterate with the array of weekdays and check if the property exists for further processing.

This approach takes the wanted order for all objects.

function iterate(object, days) {
    for (const day of days) {
        if (!(day in object)) continue;
        console.log(object[day]);       // processing
    }
}

// call
iterate(object1, arrWeekdays);

answered Feb 17 '21 at 10:00

Nina Scholz

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That is not my problem. I already know that all properties exists. But sometimes they come with different indexes in "for in " loop. I would like to sort keys in Object. – lukpar Feb 17 '21 at 10:07
it is not advisable to rely on the order of properties of objects, because they have a defined order which is maybe not the wanted one. for having an object with wanted order, you need to rebuild the object in wanted order. – Nina Scholz Feb 17 '21 at 10:13
thanks, I would do that. I thought that defined order can be sorted. – lukpar Feb 17 '21 at 10:19

SpaceNinjaApe · Accepted Answer · 2021-02-17T12:03:43.627

Short answer: There is no way you can "sort" them because there simply is no need to do so.

Anyways if you really want to place those attributes in a specific order you would have to create a new object with the desired order. Remember this order is not permanent and is most likely to change.

The ordering of object properties is non-standard in ECMAScript. You should never make assumptions about the order of elements in a JavaScript object. An Object is an unordered collection of properties. The answers below show you how to "use" sorted properties, using the help of arrays, but never actually alter the order of properties of objects themselves. So, no, it's not possible. Even if you build an object with presorted properties, it is not guaranteed that they will display in the same order in the future.

As stated in Sorting object property by values.

score 0 · Answer 3 · answered Feb 17 '21 at 10:18

We could get the entries for obj2 using Object.entries, sort them, then use Object.fromEntries to re-create it.

One has be very careful in general about depending on property order. This depends on property creation order. If you wish to iterate properties this way it's probably best to get an array of keys / entries, sort them, then iterate.

let obj2 = {
 'Donnerstag' : ['test string'],
 'Samstag' : ['test string'],
 'Montag' : ['test string'],
 'Dienstag' : ['test string'],
 'Mittwoch' : ['test string'],
 'Freitag' : ['test string']
}

let entries = Object.entries(obj2);
entries.sort(([key1, v1], [key2, v2]) => key1.localeCompare(key2));
let obj2Sorted = Object.fromEntries(entries);
console.log("Obj2, sorted:", obj2Sorted);

score 0 · Answer 4 · answered Feb 17 '21 at 10:49

Even if the properties are inserted in the right order, you still cannot (or should not) rely on it. However you can definitely implement your own iterator, here's a contrived example:

// object of days; not in "human" order
const days = {
  wed: 3,
  sat: 6,
  mon: 1,
  sun: 7,
  fri: 5,
  tue: 2,
  thu: 4
};

days[Symbol.iterator] = function* () {
  yield this.mon;
  yield this.tue;
  yield this.wed;
  yield this.thu;
  yield this.fri;
  yield this.sat;
  yield this.sun;
};


for (d of days) {
  console.log('for..of', d);
}

console.log('...days', ...days);

Javascript sort object key indexes

4 Answers4