Getting the value of an object's property wher

问题:

Given this object:

: http://www.w3.org/2005/Atom
gd: http://schemas.google.com/g/2005 
openSearch: http://a9.com/-/spec/opensearch/1.1/ 
app: http://www.w3.org/2007/app; 
media: http://search.yahoo.com/mrss/

How do I get the value of the first property? I suspect this is an easy process, but I'm drawing a blank. Thanks in advance.

The object is built as such:

Server side (php):

$namespaces = $feedXML->getNamespaces(true);
$arr = array(
'Status' => 'Success',
'Message' => 'Feed fetched.',
'Namespaces' => $namespaces,
'Feed XML' => $feedXML
);
echo json_encode($arr);

Client side (JS):

   var output = '';
    for (property in dataj["Namespaces"]) {
        output += property + ': ' + dataj["Namespaces"][property] + '; ';
    }
    alert(output);

I would like to be able to check the namespaces to see if this is Atom or RDF.

It sounds like just iterating each property is going to be the best way.

回答1:

If you're trying to get the value of the property whose key is an empty string, then you can do

var value = myObject[''];

If you try to get the "first property" of an object, you can't because properties in javascript objects aren't ordered.

回答2:

Properties aren't guaranteed to be ordered. You can however iterate over all properties to find the right one (if you know what you are looking for):

for(var prop in obj) {
    if(obj.hasOwnProperty(prop))
        doSomethingWith(obj[prop]);
}

Reference: Iterating over every property of an object in javascript using Prototype?

Then get the key by

var value = obj[key];

回答3:

You can try this code:

var test_bject = {'test': 1, 'test2': 2, 'test3': 3}, first_value;

for (i in test) {
  first_value = test_object[i];
  break;
}