Create an array based on the keys of a JavaScript object

Question

I need to create an array based on some selection of keys inside an existing constant javascript object

const EXISTING_CONSTANT_OBJECT  = {
      'fr': '10',
      'es': '15'
      'us': '10'
      'uk': '7'
      //and so on for many other iso country codes and UNPREDICTABLE key names
}

I need to be able to create an array (without modifying EXISTING_CONSTANT_OBJECT for immutability reasons) with all keys whose value are equal to 10.

For example, the expected output is

object_to_create_arr = ["fr","us"]

I tried using reduce but failed.

note: I can use ES6 and usually prefer as it's usually more concise.

use the method let arrayOfKeys = Object.keys( yourObject ) — Ricardo Gonzalez
– Ricardo Gonzalez, Commented Oct 2, 2019 at 19:46
@RicardoGonzalez not really, you did not fully read the question — epascarello
– epascarello, Commented Oct 2, 2019 at 19:55

Code Maniac · Accepted Answer · 2019-10-02 19:47:18Z

8

You can use Object.keys and filter

const obj = { 'fr': '10','es': '15','us': '10','uk': '7'}

let final = Object.keys(obj).filter(key => +obj[key] === 10)

console.log(final)

Here + is used for implicit conversion to number, because in strict equality '10' and 10 are not same

answered Oct 2, 2019 at 19:47

Code Maniac

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Comments

Neil · Accepted Answer · 2019-10-02 19:50:30Z

0

You're on the right track with reduce. As mentioned with other answers, you can also use filter (which might actually be better).

Here is a solution using reduce

const obj  = {
  'fr': '10',
  'es': '15',
  'us': '10',
  'uk': '7'
}

let result = Object.keys(obj).reduce((acc, curr) => {
  if (parseInt(obj[curr], 10) === 10) {
    acc.push(curr)
  }
  return acc
}, [])

console.log(result)

answered Oct 2, 2019 at 19:50

Neil

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3 Comments

Mathieu Over a year ago

Thanks i really hesitated between your solution and @code maniac but his one is more concise and equally correct

Neil Over a year ago

no problem, they both achieve the same result! Just wanted to show how it can be done with reduce

Mathieu Over a year ago

Sure, appreciate it

Martin · Accepted Answer · 2019-10-02 19:51:07Z

0

Try this

function createArr(obj){
    let arr = [];
    for (let key in obj) if (obj.hasOwnProperty(key) && String(obj[key]) === '10') arr.push(key);
    return arr;
}

answered Oct 2, 2019 at 19:51

Martin

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Comments

mwilson · Accepted Answer · 2019-10-02 19:52:16Z

0

Object.keys(<object>) will do the trick BTW: Your object is invalid. You're missing some commas.

const EXISTING_CONSTANT_OBJECT = {
  'fr': '10',
  'es': '15',
  'us': '10',
  'uk': '7'
  //and so on for many other iso country codes and UNPREDICTABLE key names
};

const keys = Object.keys(EXISTING_CONSTANT_OBJECT);
console.log(keys);

If you want to just get the keys where the value is 10, it's just as simple as adding .filter

const EXISTING_CONSTANT_OBJECT = {
  'fr': '10',
  'es': '15',
  'us': '10',
  'uk': '7'
};

const keysWith10 = Object.keys(EXISTING_CONSTANT_OBJECT).filter(k => EXISTING_CONSTANT_OBJECT[k] === '10');
console.log(keysWith10);

edited Oct 2, 2019 at 19:52

answered Oct 2, 2019 at 19:47

mwilson

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Comments

Harshit Agarwal · Accepted Answer · 2019-10-02 19:59:25Z

0

Object.keys() function returns the array of values corresponding to the keys of object you feed to this function. For example:

let yourObject = { key1: value1, key2: value2, key3:value3}
let arr = Object.keys(yourObject)
console.log(arr) // Output: [ 'key1', 'key2', 'key3']

Hope this helps!!

answered Oct 2, 2019 at 19:59

Harshit Agarwal

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