Get key using value from an object in JavaScript?

Question

c =      {
            "UNKNOWN_ERR" : 0,
            "INDEX_SIZE_ERR" : 1,
            "DOMSTRING_SIZE_ERR" : 2,
            "HIERARCHY_REQUEST_ERR" : 3,
            "WRONG_DOCUMENT_ERR" : 4,
            "INVALID_CHARACTER_ERR" : 5,
            "NO_DATA_ALLOWED_ERR" : 6,
            "NO_MODIFICATION_ALLOWED_ERR" : 7,
            "NOT_FOUND_ERR" : 8,
            "NOT_SUPPORTED_ERR" : 9}

To get the value using the key is easy, I just use the key in c["UNKNOWN_ERR"] to get 0, given that all the values are unique is safe to get the key (message) from the value(errorcode).

Is there a standard way to do that or do I need to write a function that looks in all key and search that specific value?

Possible duplicate of [best way to get the key of a key/value javascript object](http://stackoverflow.com/questions/6268679/best-way-to-get-the-key-of-a-key-value-javascript-object) — Andy, Feb 04 '16 at 18:03
Probably a duplicate of https://stackoverflow.com/questions/9907419/how-to-get-a-key-in-a-javascript-object-by-its-value — , Jul 04 '19 at 10:29

score 18 · Accepted Answer · answered Nov 07 '12 at 16:38

18

As you already assumed you need to iterate over the object's attributes and check the value.

for(var key in c) {
    if(c[key] === whatever) {
        // do stuff with key
    }
}

answered Nov 07 '12 at 16:38

ThiefMaster

310,957
84
592
636

score 13 · Answer 2 · answered Jan 10 '17 at 11:35

13

es6 find method:

const getKey = (obj,val) => Object.keys(obj).find(key => obj[key] === val);

in your case

console.log(getKey(c,1)); // INDEX_SIZE_ERR

answered Jan 10 '17 at 11:35

Fareed Alnamrouti

30,771
4
85
76

This doesn't work when the value is 0 – Non404 Sep 29 '22 at 10:26

score 6 · Answer 3 · answered Jan 24 '14 at 11:22

6

Underscore provides a more easy solution to this

You can get key using this code also

var errKey = _.invert(c)[errCode];

for e.x. if you use errCode = 3 as shown below

var errKey = _.invert(c)[3];

then

errKey will be HIERARCHY_REQUEST_ERR

answered Jan 24 '14 at 11:22

Pratik

1,531
3
25
57

ns16 · Answer 4 · 2019-03-27T16:03:42.433

2

Try findKey() lodash method:

var key = _.findKey(c, v => v === val)

where val - property value.

edited Mar 27 '19 at 16:03

answered Nov 21 '17 at 13:00

ns16

1,322
2
17
26

The original question does not seem to ask about external libraries. – Matteo Nov 21 '17 at 13:30

Get key using value from an object in JavaScript?

4 Answers4