How to get first member of an object in javascript

Question

Possible Duplicate:
Access the first property of an object

I have a javascript object like this:

var list = {
    item1: "a",
    item2: "b",
    item3: "c",
    item4: "d"
};

Using reflection in JS, I can say list["item1"] to get or set each member programmatically, but I don't want to rely on the name of the member (object may be extended). So I want to get the first member of this object.

If I write the following code it returns undefined. Anybody knows how this can be done?

var first = list[0]; // this returns undefined

http://stackoverflow.com/questions/2342371/jquery-loop-on-json-data-using-each — Jack, Sep 25 '11 at 11:30
But what if you change the code that initialises that object. Surely it's better to reference it by name, or use an array? — Bojangles, Sep 25 '11 at 11:34

score 41 · Accepted Answer · answered Sep 25 '11 at 11:31

41

 for(var key in obj) break;
 // "key" is the first key here

answered Sep 25 '11 at 11:31

user187291

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That's a very smart solution. – Fab Fuerste Dec 19 '19 at 13:12

score 11 · Answer 2 · answered Sep 25 '11 at 11:31

11

var list = {
    item1: "a",
    item2: "b",
    item3: "c",
    item4: "d"
};

is equivalent to

var list = {
    item2: "b",
    item1: "a",
    item3: "c",
    item4: "d"
};

So there is no first element. If you want first element you should use array.

answered Sep 25 '11 at 11:31

Petar Ivanov

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That's right, but stereofrog's answer gives me what I want!. I wouldn't say "there is no first", I would say "there is no ordering or indexing on object members". Anything coming first is first any way. – Mo Valipour Sep 25 '11 at 11:39
@valipour: So why does your question say *"I want to get the first member of this object"* if you don't care if you get the first item as defined by your ordering? Now it sounds like you're actually asking for a single member, irrespective of the order you defined. – user113716 Sep 25 '11 at 12:49

score 2 · Answer 3 · edited Sep 25 '11 at 11:34

2

Even though some implementations of JavaScript uses lists to make object, they are supposed to be unordered maps.

So there is no first one.

edited Sep 25 '11 at 11:34

pimvdb

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answered Sep 25 '11 at 11:32

megakorre

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2

That's right, but stereofrog's answer gives me what I want!. I wouldn't say "there is no first", I would say "there is no ordering or indexing on object members". Anything coming first is first any way. – Mo Valipour Sep 25 '11 at 11:40

score 0 · Answer 4 · edited May 23 '17 at 12:33

0

How do I loop through or enumerate a JavaScript object?

You can use the following to get the desired key.

for (var key in p) {
  if (p.hasOwnProperty(key)) {
    alert(key + " -> " + p[key]);
  }
}

You need to use an array if you want to access elements in an indexed way.

edited May 23 '17 at 12:33

Community

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answered Sep 25 '11 at 11:33

Jack

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How to get first member of an object in javascript

4 Answers4