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Get an object in an array with one of your fields

Sorry I'm new to JS; I have an array of objects; how can i get the name of an object that has key "user_key3" and obviously has no loop and has a condition.

arr = [{
        "name": "user1",
        "key": "user_key1"
},{
        "name": "user3",
        "key": "user_key3"
},{
        "name": "user2",
        "key": "user_key2"
}]

Please let me know if you need more clarification.

thank

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7 replies


An inefficient but concise solution would be



var keyarr = arr.map(function(x) { return x.key } );
//keyarr is list of keys
var index=keyarr.indexOf("user_key3");
//arr[index] is your answer. Index will be -1 if the key doesn't exist
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You will have to iterate over and check the key

var user_name;

for (var i=0; i<arr.length; i++) {
    if ( arr[i].key === 'user_key3' ) {
        user_name = arr[i].name;
        break;
    }
}

FIDDLE



You edited the question to include

obviously without a loop and has the condition

but loop and condition is by far the most efficient and cross-browser way to do it, so why don't you "explicitly" want it?

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You can do it functionally like this

var name;
arr.forEach(function(currentObject) {
    if (currentObject.key === "user_key3") {
        name = currentObject.name;
    }
});

If you want to short-circuit on the first match, you can use Array.prototype.some

like this

var name;
arr.some(function(currentObject) {
    if (currentObject.key === "user_key3") {
        name = currentObject.name;
        return true;
    }
    return false;
});
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The OP mentioned is obviously no loop and has a condition . I would do it like below:

arr = [{
    "name": "user1",
    "key": "user_key1"
},{
    "name": "user3",
    "key": "user_key3"
},{
    "name": "user2",
    "key": "user_key2"
}];

var keyValMap = arr.map(function(n) { return n.key } );
var arrIndex = keyValMap.indexOf('user_key3');
alert(arr[arrIndex].name);

Fiddle

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In general, finding an element that satisfies some arbitrary property in an array requires you to iterate over the array:

function find(arr, name) {
  for (var i=0; i<arr.length; i++) {
    if ( arr[i].key === name ) {
      return arr[i];
    }
  }
}

Then, to find him,

var obj = find(arr, 'user_key3');

Using more functional solutions to find an item is fine too, but you end up getting stuck in a loop anyway.

However, if you are searching by key, then an array of key-value pairs is not the best data structure. I would suggest using the object directly:

var map = {
  'user_key1': 'user1',
  'user_key2': 'user2',
  'user_key3': 'user3'
}

Then the search is simple:

map['user_key3'];
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Try this - underscore.js

For your example -

_.where(arr, {key: "user_key3"});
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You cannot do this kind of thing with objects in Javascript. Although here you have a combination of callbacks and a loop:

arr = [{
        "name": "user1",
        "key": "user_key1"
  },{
        "name": "user3",
        "key": "user_key3"
},{
        "name": "user2",
        "key": "user_key2"
}];

arr.forEach(function(elme){

   for(var g in elme)
   {  
     if(elme[g] == 'user_key3') 
     {
       console.log("Found the value: "+g+" : "+elme[g]);
     };
   }
});
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