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

console.log(Object.keys(obj));
console.log(Object.keys(obj).length)

现代浏览器支持:

Var obj = { key1:“value1”, key2: value2, key3:“value3”, key4:“value4” ｝ console.log(种(obj)); //我们也可以得到值 console.log (Object.values (obj));

如果你决定使用Underscore.js，你最好这样做

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

var keys = [];
_.each( obj, function( val, key ) {
    keys.push(key);
});
console.log(keys.lenth, keys);

如果你只想要特定于特定对象的键，而不是任何派生的原型属性:

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

e.g:

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

var keys = new Array();
for(var key in obj)
{
   keys[keys.length] = key;
}

var keyLength = keys.length;

要从对象中访问任何值，可以使用obj[key];

Anurags的回答基本上是正确的。 但是为了在旧的浏览器中也支持Object.keys(obj)，你可以使用下面的代码 https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys ． 如果浏览器中没有Object.keys(obj)方法，它会添加该方法。

if (!Object.keys) {
 Object.keys = (function() {
 'use strict';
 var hasOwnProperty = Object.prototype.hasOwnProperty,
    hasDontEnumBug = !({ toString: null }).propertyIsEnumerable('toString'),
    dontEnums = [
      'toString',
      'toLocaleString',
      'valueOf',
      'hasOwnProperty',
      'isPrototypeOf',
      'propertyIsEnumerable',
      'constructor'
    ],
    dontEnumsLength = dontEnums.length;

return function(obj) {
  if (typeof obj !== 'object' && (typeof obj !== 'function' || obj === null)) {
    throw new TypeError('Object.keys called on non-object');
  }

  var result = [], prop, i;

  for (prop in obj) {
    if (hasOwnProperty.call(obj, prop)) {
      result.push(prop);
    }
  }

  if (hasDontEnumBug) {
    for (i = 0; i < dontEnumsLength; i++) {
      if (hasOwnProperty.call(obj, dontEnums[i])) {
        result.push(dontEnums[i]);
      }
    }
  }
  return result;
};
}());
}