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If I have an object such that

var object = function(key,text) { this.key = key; this.text = text; }

And create an array of these objects

var objArray = []; objArray[0] = new object('key1','blank'); objArray[1] = new object('key2','exampletext'); objArray[2] = new object('key3','moretext');

is there a way that I can retrieve only one of the properties of all of the objects in the array? For example:

var keyArray = objArray["key"];

The above example doesn't return set keyArray to anything, but I was hoping it would be set to something like this:

keyArray = [ 'key1', 'key2', 'key3']

Does anyone know of a way to do this without iterating through the objArray and manually copying each key property to the key array?

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56

This is easily done with the Array.prototype.map() function:

var keyArray = objArray.map(function(item) { return item["key"]; });

If you are going to do this often, you could write a function that abstracts away the map:

function pluck(array, key) { return array.map(function(item) { return item[key]; }); }

In fact, the Underscore library has a built-in function called pluck that does exactly that.

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IE 8 and below does not support map
The MDN documentation linked above includes a polyfill for IE8 and below.
function pluck(obj){return obj[this]} allows r.map(pluck,"key")
@dandavis: agreed, that composes much more nicely (you can call r.filter(pluck, "key") to find items with a given key, for example). My version merely approximates what Underscore's _.pluck does.
Sometimes I want to do something similar (keep only certain properties in a JavaScript object): stackoverflow.com/a/67591318/470749
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var object = function(key,text) { this.key = key; this.text = text; } var objArray = []; objArray[0] = new object('key1','blank'); objArray[1] = new object('key2','exampletext'); objArray[2] = new object('key3','moretext'); var keys = objArray.map(function(o,i) { return o.key; }); console.log(keys); // ["key1", "key2", "key3"]

JS Bin Example

http://jsbin.com/vamey/1/edit

Note that older browsers may not support map but you can easily do this with a for loop:

var keys = []; for (var i = 0; i < objArray.length; i++) { keys.push(objArray[i].key); }

JS Bin Example

http://jsbin.com/redis/1/edit

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1

You would want to do something like this:

objArray.map(function (obj) { return obj.key; });

Here is a JSFiddle to demo: http://jsfiddle.net/Q7Cb3/

If you need older browser support, you can use your own method:

JSFiddle demo: http://jsfiddle.net/Q7Cb3/1/

function map (arr, func) { var i = arr.length; arr = arr.slice(); while (i--) arr[i] = func(arr[i]); return arr; }
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Note older browsers may not support map.
0

Well something has to iterate through the elements of the array. You can use .map() to make it look nice:

var keys = objArray.map(function(o) { return o.key; });

You could make a function to generate a function to retrieve a particular key:

function plucker(prop) { return function(o) { return o[prop]; }; }

Then:

var keys = objArray.map(plucker("key"));
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Really "objArray" is an array that have 3 objects inside, if you want list of keys, you can try this:

var keys = []; for(a in objArray) { keys.push(objArray[a].key); }

You have in var keys, the three keys.

Hope that helps! :)

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It is bad practice in JavaScript to use for ... in to iterate through arrays.
for(var a = 0; a < objArray.lenght; a++){..} better, sorry. :)

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