I have the following objects:

const allMembers = {
    "-Lz8YxHiwp8QZW3TqAFn": {
        "first": "foo",
        "last": "bar",
        "uid": "-Lz8YxHiwp8QZW3TqAFn"
    },
    "-Lz8YxHqQXWoaGOFRLrO": {
        "first": "foo",
        "last": "bar",
        "uid": "-Lz8YxHqQXWoaGOFRLrO"
    },
    "-Lz8YxHsMItaaTVNyQRE": {
        "first": "foo",
        "last": "bar",
        "uid": "-Lz8YxHsMItaaTVNyQRE"
    },
    "-Lz8YxHwuVBMWl0Go6C5": {
        "first": "foo",
        "last": "bar",
        "uid": "-Lz8YxHwuVBMWl0Go6C5"
    },
    "-Lz8YxHy0S-QkDaE1PkX": {
        "first": "foo",
        "last": "bar",
        "uid": "-Lz8YxHy0S-QkDaE1PkX"
    },
}

const attendanceData = {
    "-Lz8YxHiwp8QZW3TqAFn": true,
    "-Lz8YxHqQXWoaGOFRLrO": true,
    "-Lz8YxHsMItaaTVNyQRE": true,
    "-Lz8YxHwuVBMWl0Go6C5": false,
    "-Lz8YxHy0S-QkDaE1PkX": true,
    "-Lz8YxIFA1XGVmaNfNr3": false,
    "-Lz8YxIJVZnIIj7RgEzg": false,
}

I need to clean up the allMembers to only return if it's found as true in attendanceData. Here is my attempt but it's obviously not working. Also the way I'm doing it has to loop the first one over the other times.

const membersHere = Object.keys(allMembers).filter(memEl => Object.keys(attendanceData).find(attendEl => memEl == attendEl));

I have the following objects:

const allMembers = {
    "-Lz8YxHiwp8QZW3TqAFn": {
        "first": "foo",
        "last": "bar",
        "uid": "-Lz8YxHiwp8QZW3TqAFn"
    },
    "-Lz8YxHqQXWoaGOFRLrO": {
        "first": "foo",
        "last": "bar",
        "uid": "-Lz8YxHqQXWoaGOFRLrO"
    },
    "-Lz8YxHsMItaaTVNyQRE": {
        "first": "foo",
        "last": "bar",
        "uid": "-Lz8YxHsMItaaTVNyQRE"
    },
    "-Lz8YxHwuVBMWl0Go6C5": {
        "first": "foo",
        "last": "bar",
        "uid": "-Lz8YxHwuVBMWl0Go6C5"
    },
    "-Lz8YxHy0S-QkDaE1PkX": {
        "first": "foo",
        "last": "bar",
        "uid": "-Lz8YxHy0S-QkDaE1PkX"
    },
}

const attendanceData = {
    "-Lz8YxHiwp8QZW3TqAFn": true,
    "-Lz8YxHqQXWoaGOFRLrO": true,
    "-Lz8YxHsMItaaTVNyQRE": true,
    "-Lz8YxHwuVBMWl0Go6C5": false,
    "-Lz8YxHy0S-QkDaE1PkX": true,
    "-Lz8YxIFA1XGVmaNfNr3": false,
    "-Lz8YxIJVZnIIj7RgEzg": false,
}

I need to clean up the allMembers to only return if it's found as true in attendanceData. Here is my attempt but it's obviously not working. Also the way I'm doing it has to loop the first one over the other times.

const membersHere = Object.keys(allMembers).filter(memEl => Object.keys(attendanceData).find(attendEl => memEl == attendEl));

• javascript

• What result do you actually want? If it's just the list of IDs then: Object.keys(allMembers).filter(m => attendanceData[m]) – jarmod Commented May 26, 2022 at 19:39

3 Answers 3

• Convert the allMembers object into an array of key value pairs using Object.entries.

• Filter the items that have value true using Array.prototype.filter.

• Transform the array back to an object using Object.fromEntries.

const 
  allMembers = {'-Lz8YxHiwp8QZW3TqAFn': {first: 'foo',last: 'bar',uid: '-Lz8YxHiwp8QZW3TqAFn'},'-Lz8YxHqQXWoaGOFRLrO': {first: 'foo',last: 'bar',uid: '-Lz8YxHqQXWoaGOFRLrO'},'-Lz8YxHsMItaaTVNyQRE': {first: 'foo',last: 'bar',uid: '-Lz8YxHsMItaaTVNyQRE'},'-Lz8YxHwuVBMWl0Go6C5': {first: 'foo',last: 'bar',uid: '-Lz8YxHwuVBMWl0Go6C5'},'-Lz8YxHy0S-QkDaE1PkX': {first: 'foo',last: 'bar',uid: '-Lz8YxHy0S-QkDaE1PkX'}},
  attendanceData = {'-Lz8YxHiwp8QZW3TqAFn': true,'-Lz8YxHqQXWoaGOFRLrO': true,'-Lz8YxHsMItaaTVNyQRE': true,'-Lz8YxHwuVBMWl0Go6C5': false,'-Lz8YxHy0S-QkDaE1PkX': true,'-Lz8YxIFA1XGVmaNfNr3': false,'-Lz8YxIJVZnIIj7RgEzg': false},
  filteredMembers = Object.fromEntries(
    Object.entries(allMembers).filter(([k]) => attendanceData[k])
  );

console.log(filteredMembers);

You can also do it using Array.prototype.reduce

const 
  allMembers = {'-Lz8YxHiwp8QZW3TqAFn': {first: 'foo',last: 'bar',uid: '-Lz8YxHiwp8QZW3TqAFn'},'-Lz8YxHqQXWoaGOFRLrO': {first: 'foo',last: 'bar',uid: '-Lz8YxHqQXWoaGOFRLrO'},'-Lz8YxHsMItaaTVNyQRE': {first: 'foo',last: 'bar',uid: '-Lz8YxHsMItaaTVNyQRE'},'-Lz8YxHwuVBMWl0Go6C5': {first: 'foo',last: 'bar',uid: '-Lz8YxHwuVBMWl0Go6C5'},'-Lz8YxHy0S-QkDaE1PkX': {first: 'foo',last: 'bar',uid: '-Lz8YxHy0S-QkDaE1PkX'}},
  attendanceData = {'-Lz8YxHiwp8QZW3TqAFn': true,'-Lz8YxHqQXWoaGOFRLrO': true,'-Lz8YxHsMItaaTVNyQRE': true,'-Lz8YxHwuVBMWl0Go6C5': false,'-Lz8YxHy0S-QkDaE1PkX': true,'-Lz8YxIFA1XGVmaNfNr3': false,'-Lz8YxIJVZnIIj7RgEzg': false},
  filteredMembers = Object.entries(allMembers).reduce(
    (r, [k, v]) => (attendanceData[k] && (r[k] = v), r),
    {}
  );

console.log(filteredMembers);

Other relevant documentations:

• Comma operator (,)

You can use reduce method:

const allMembers = {
    "-Lz8YxHiwp8QZW3TqAFn": {
        "first": "foo",
        "last": "bar",
        "uid": "-Lz8YxHiwp8QZW3TqAFn"
    },
    "-Lz8YxHqQXWoaGOFRLrO": {
        "first": "foo",
        "last": "bar",
        "uid": "-Lz8YxHqQXWoaGOFRLrO"
    },
    "-Lz8YxHsMItaaTVNyQRE": {
        "first": "foo",
        "last": "bar",
        "uid": "-Lz8YxHsMItaaTVNyQRE"
    },
    "-Lz8YxHwuVBMWl0Go6C5": {
        "first": "foo",
        "last": "bar",
        "uid": "-Lz8YxHwuVBMWl0Go6C5"
    },
    "-Lz8YxHy0S-QkDaE1PkX": {
        "first": "foo",
        "last": "bar",
        "uid": "-Lz8YxHy0S-QkDaE1PkX"
    },
}

const attendanceData = {
    "-Lz8YxHiwp8QZW3TqAFn": true,
    "-Lz8YxHqQXWoaGOFRLrO": true,
    "-Lz8YxHsMItaaTVNyQRE": true,
    "-Lz8YxHwuVBMWl0Go6C5": false,
    "-Lz8YxHy0S-QkDaE1PkX": true,
    "-Lz8YxIFA1XGVmaNfNr3": false,
    "-Lz8YxIJVZnIIj7RgEzg": false,
}

const reduced = Object.entries(allMembers).reduce((data, [key, value]) => {
  if (attendanceData[key] ?? false)
    data[key] = value;
  return data;  
}, {});

console.log(reduced);

You can bine Object.keys(), Array.prototype.filter() and Array.prototype.reduce()

Code:

const allMembers = {'-Lz8YxHiwp8QZW3TqAFn': {first: 'foo',last: 'bar',uid: '-Lz8YxHiwp8QZW3TqAFn',},'-Lz8YxHqQXWoaGOFRLrO': {first: 'foo',last: 'bar',uid: '-Lz8YxHqQXWoaGOFRLrO',},'-Lz8YxHsMItaaTVNyQRE': {first: 'foo',last: 'bar',uid: '-Lz8YxHsMItaaTVNyQRE',},'-Lz8YxHwuVBMWl0Go6C5': {first: 'foo',last: 'bar',uid: '-Lz8YxHwuVBMWl0Go6C5',},'-Lz8YxHy0S-QkDaE1PkX': {first: 'foo',last: 'bar',uid: '-Lz8YxHy0S-QkDaE1PkX',},}

const attendanceData = {'-Lz8YxHiwp8QZW3TqAFn': true,'-Lz8YxHqQXWoaGOFRLrO': true,'-Lz8YxHsMItaaTVNyQRE': true,'-Lz8YxHwuVBMWl0Go6C5': false,'-Lz8YxHy0S-QkDaE1PkX': true,'-Lz8YxIFA1XGVmaNfNr3': false,'-Lz8YxIJVZnIIj7RgEzg': false,}
  
const result = Object
  .keys(allMembers)
  .filter((k) => attendanceData[k])
  .reduce((a, k) => (a[k] = allMembers[k], a), {})

console.log(result)