How can I get a key name (in a hash) by using its value?

Question

I understand this is a little unorthodox.

Lets say I have this hash.

 someHash = {
    'item1' => '5',
    'item2' => '7',
    'item3' => '45',
    'item4' => '09'
}

Using native js, or prototype or Jquery -- is there a method that will enable me to get the "key name" by just having the value?

I don't want all the keys, just the one that matches my value. Sorta of a like a map in reverse?

I am getting a return from the db which I get a "value" and I have to match that value with some js hash on the front end.

So the app hands me "45"... Is there a way to use js (prototype or jquery) to then get the key "item3"?

Solution 1

In order to get the keys which map to a given value you'll need to search the object properties. For example

function getKeysForValue(obj, value) {
  var all = [];
  for (var name in obj) {
    if (Object.hasOwnProperty(name) && obj[name] === value) {
      all.push(name);
    }
  }
  return all;
}

Solution 2

Using underscore.js:

_.invert(someHash)[value]

Solution 3

There is no direct method but you can try something like this.

var key;
$.each(someHash, function(key, val){
    if(val == 'valToCompare'){
        key = key;
        return false;
    }
});

Solution 4

Without uniqueness you can get the first:

var hash = {item1: 0, item2: 1},
    value = 1,
    key;
for(var i in hash)
{
    if (hash.hasOwnProperty(i) && hash[i] === value) {
        key = i;
        break;
    }
}
key; // item2

hasOwnProperty ensures that hash has the property not a prototype.

break stops the loop once a key is found.

Solution 5

I don't know of a native answer, but you could write your own:

var someHash = {
  'item1' : '5',
  'item2' : '7',
  'item3' : '45',
  'item4' : '09'
};

function getKeyByValue(hash, value) {
  var key;
  for(key in hash) {
    if (hash[key] == value) return key;
  }
}

alert(getKeyByValue(someHash, '7'));

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