How to get first member of an object in javascript [duplicate]

This question already has answers here: Closed 11 years ago.

Possible Duplicate:

Access the first property of an object

I have a javascript object like this:

v开发者_C百科ar 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

---

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

---

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.

---

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

So there is no first one.

---

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.