如何使用其值获取密钥名称（在哈希中）？

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"?

Answer 1

使用underscore.js：

_.invert(someHash)[value]

Answer 2

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;
}

Answer 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;
    }
});

Answer 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.

Answer 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'));

Answer 6

Perhaps array_flip could help you. This makes a new array where the keys are the values and vice versa. Then, just look for the key in that new array, and the resulting value is the key in the original array you were looking for.

Answer 7

Loop through the object.

function findInObj(obj, needle)
    for(var x in obj){
      if(obj.x==needle) return x;
    }
    return false;
}

Answer 8

Since more than one property in an object can have the same value, you could return an array of the property names that match the value.

var someHash={
    'item1':'5',
    'item2':'7',
    'item3':'45',
    'item4':'09',
    'item5':'7'
}
function hasAny(what){
    var names= [];
    for(var p in this){
        if(this[p]=== what) names.push(p);
    }
    return names;
}

hasAny.call(someHash, '7');

/* returned value: (Array) item2,item5 */