How can I get object's property name by its value [JS]

Question

questions={
     1:{
          quest: "blah blah blah",
          answers: ["1812", "1837", "1864", "1899"],
          correct: "1837"
     },
     2:{
         quest: "fasfa asf",
         answers : ["2","3","4","5"],
         correct : "3"
     }
 }

For example, I know value of 1. I need to get that object's name with its value. var x = {quest: "blah blah blah", answers: ["1812", "1837", "1864", "1899"], correct: "1837"}

returnNameOf(x) expected output 1;

You want to get output as `1` when input is `{quest: "blah blah blah", answers: ["1812", "1837", "1864", "1899"], correct: "1837"}`? — Maheer Ali, Mar 11 '19 at 17:21
Does `x` *point to* the question or is it another object with the same values? — Jonas Wilms, Mar 11 '19 at 17:21
What do you get when you do `x === questions[1]` ? `true` or `false` ? — Jonas Wilms, Mar 11 '19 at 17:23
Could you just use `quest` as the key instead of the whole object? — IllusiveBrian, Mar 11 '19 at 17:30

score 1 · Accepted Answer · answered Mar 11 '19 at 17:26

You can use find() on Object.keys() and compare objects using JSON.stringify()

let questions={
     1:{
          quest: "blah blah blah",
          answers: ["1812", "1837", "1864", "1899"],
          correct: "1837"
     },
     2:{
         quest: "fasfa asf",
         answers : ["2","3","4","5"],
         correct : "3"
     }
 }
 
 let val = {
         quest: "fasfa asf",
         answers : ["2","3","4","5"],
         correct : "3"
     }
function getKey(obj,value){
  if(typeof value === "object"){
    value = JSON.stringify(value);
    return Object.keys(obj).find(key => JSON.stringify(obj[key]) === value);
  }
  else return Object.keys(obj).find(key => obj[key] === value);
}

console.log(getKey(questions,val));

Do caching `Object.keys(obj)` helps in any way? – brk Mar 11 '19 at 17:42 — brk, Mar 11 '19 at 17:42

brk · Answer 2 · 2019-03-11T17:24:46.550

You can convert the object to string and use in comparison. So in this example we need to find the key whose value matches with toMatch. Therefore in the function toMatch is converted to string since object matching or object equality test will return false as they compare memory location

let toMatch = {
  quest: "blah blah blah",
  answers: ["1812", "1837", "1864", "1899"],
  correct: "1837",
};

let questions = {
  1: {
    quest: "blah blah blah",
    answers: ["1812", "1837", "1864", "1899"],
    correct: "1837"
  },
  2: {
    quest: "fasfa asf",
    answers: ["2", "3", "4", "5"],
    correct: "3"
  }
}


function findKey(objString) {
  let val = JSON.stringify(toMatch)
  for (let keys in questions) {
    if (JSON.stringify(questions[keys]) === val) {
      return keys;
    }
  }
}

console.log(findKey(toMatch))

It works, but my json file contains much more objects and comparison will be too slow. — Kim Ber, Mar 11 '19 at 17:24

score 0 · Answer 3 · answered Mar 11 '19 at 17:23

0

You could search in the Objects entries:

const key = 0, value = 1;

const result = Object.entries(questions).find(it => it[value] === x)[key];

answered Mar 11 '19 at 17:23

Jonas Wilms

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How can I get object's property name by its value [JS]

3 Answers3