in JavaScript get first object member name

Question

Possible Duplicate:
Access the first property of an object

I just want to know if there is a better way to get the first member name in a object like:

var x={a:1};
func(x);//will return 'a'

I programmed a small function but I'm not satisfied, i think that there is a better way

what i did is :

var get_member = function(obj){for (i in obj){if (obj.hasOwnProperty(i)) return i;}};

the "first element" is not a reliable concept for an object. it's not like an array. This is a MU-question :) — Fabrizio Calderan loves trees, Sep 20 '12 at 10:40
see http://stackoverflow.com/questions/5525795/does-javascript-guarantee-object-property-order — Alex Pacurar, Sep 20 '12 at 10:45

score 0 · Answer 1 · edited May 23 '17 at 12:21

Supposing your "first member" is defined by addition order :

There is no guaranteed order in javascript object properties, so you shouldn't do this even while it currently work on most browsers.

Look at this related question : Elements order in a "for (… in …)" loop

So the proper ECMAScript compliant implementation for first added member can't exist.

Supposing you have an intrinsic "first member" definition based on key (or value) :

If what you want is based on a given order, let's say alphabetical for example, you can do this :

var keys = [];
for (k in x) {
   keys.push(k);   
}
keys.sort();
return keys[0];

score 0 · Answer 2 · answered Sep 20 '12 at 10:45

There is no "first" property of an object, they have no order. You can only get "some" property by using

function func(obj) {
    if (Object(obj) !== obj)
        throw new Error("not an object");
    for (var prop in obj)
        return prop;
    return null;
}

score 0 · Answer 3 · answered Sep 20 '12 at 11:02

0

I think it's the better way to get the first key from the object.

var x= {a:1};

for (var key in x) break;

console.log(key);

answered Sep 20 '12 at 11:02

kannanrbk

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in JavaScript get first object member name

3 Answers3