获取JavaScript对象键列表

Question

我有一个像JavaScript的对象

var obj = {
   key1: 'value1',
   key2: 'value2',
   key3: 'value3',
   key4: 'value4'
}

如何获取此对象中的长度和键列表？

Answer 1

var obj = {
   key1: 'value1',
   key2: 'value2',
   key3: 'value3',
   key4: 'value4'
}
var keys = Object.keys(obj);
console.log('obj contains ' + keys.length + ' keys: '+  keys);

它现在支持大多数主流浏览器.

Answer 2

var obj = {
   key1: 'value1',
   key2: 'value2',
   key3: 'value3',
   key4: 'value4'
};
var keys = [];

for (var k in obj) keys.push(k);

alert("total " + keys.length + " keys: " + keys);

Answer 3

Underscore.js使转换非常干净:

var keys = _.map(x, function(v, k) { return k; });

编辑:我错过了你也可以这样做:

var keys = _.keys(x);

Answer 4

如果您只想要特定于该特定对象的键而不是任何派生prototype属性:

function getKeys(obj) {
    var r = []
    for (var k in obj) {
        if (!obj.hasOwnProperty(k)) 
            continue
        r.push(k)
    }
    return r
}

例如:

var keys = getKeys({'eggs': null, 'spam': true})
var length = keys.length // access the `length` property as usual for arrays