Get all keys of a JavaScript object whose value is true

Question

I have the object pks and would like to extract all keys where the value is true.

pks = {3: false, 7: true, 2: true}

Is there an underscore function that can return [7, 2]? I’ve tried _.invert but I lost one of the values in the process so I’m looking for an alternative.

Answer 1

You can do this with builtin functions, no need for Underscore:

Object.keys(pks)
  .filter(function(k){return pks[k]})
  .map(Number)

Answer 2

Try this:

_.reduce(pks, function(memo, val, key){
  if (val) memo.push(key);
  return memo;
}, []);

Answer 3

Lodash:

_.compact(_.map(pks, function(value, prop) {
  if(value) {
    return prop;
  }
}));

Answer 4

I would use Object.entries(), filter() and map():

const pks = {3: false, 7: true, 2: true};

const trueKeys = Object.entries(pks).filter(([_, v]) => v).map(([k, _]) => +k);

console.log(trueKeys);