How to get a key from array of objects by its value Javascript

Question

I have a collection which looks like this:

    var array = [
     { 'key1': 'val1'},
     { 'key2': 'val2'}
    ];

I want a function which takes array and value as parameters and returns key of that value (values are unique)

 getKey(array, 'val1');
 >>>>> output: 'key1'

I tried the following solution but it says key property is not defined:

         getKey(array, value) {
            var keys = [];
            array.forEach(function(element) {
                for (key in element) {
                    if(value == element[key]) {
                        keys.push(key);
                    }
                }
            })

            return keys[0];
        },

Answer 1

Create an inverse object with value as key and key as value . And then finally access the value from object as key.

 var array = [{ 'key1': 'val1'},{ 'key2': 'val2'}]; function getKey(arr, val) { let obj = arr.reduce((a,c) => { Object.entries(c).forEach(([k,v]) => a[v]=k); return a; }, {}) return obj[val]; } console.log(getKey(array, 'val1'));

Answer 2

 var arr = [{ 'key1': 'val1'}, { 'key2': 'val2'}]; function getKey(data,value) { let keys=[]; data.forEach(function(element) { for (key in element) { if(element[key]==value) keys.push(key); } }); return keys } console.log(getKey(arr, 'val1'))

Answer 3

You can also try this:

 var arr = [{ 'key1': 'val1'}, { 'key2': 'val2'}]; function getKey(arr, val) { var result = 'not found'; arr.forEach(obj => { for (var key in obj) { if(obj[key] === val) result = key; } }); return result; } console.log(getKey(arr, 'val1')); console.log(getKey(arr, 'value'));

Answer 4

In pure JS you can take all the entries, flatten them and simply search the value in all couples and if found then just take the first entry of that couple.

[].concat(...array.map(Object.entries)).find(a=>a[1]=='val1')[0]

Here is an working example:

 var array = [{'key1': 'val1'}, {'key2': 'val2'}, {'key3': 'val3'}], getKey = (arr,v)=>[].concat(...arr.map(Object.entries)).find(a=>a[1]==v)[0]; console.log(getKey(array, 'val2')); console.log(getKey(array, 'val3'));

However, I will suggest you to use lodash (or underscore , or lazy ) to make it more cleaner and simple.

Here is a lodash approach:

_.findKey(_.merge({}, ...array), s=>s=='val1')

Here is a woking example:

 var array = [{'key1': 'val1'}, {'key2': 'val2'}, {'key3': 'val3'}], getKey = (arr,v)=>_.findKey(_.merge({}, ...arr), s=>s==v); console.log(getKey(array, 'val2')); console.log(getKey(array, 'val3'));

 <script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js"></script>