在Javascript中，如果有一个对象具有很多作为函数的属性，那么如何将它们转换为（函数名称的）字符串数组？

Question

In Javascript, if an object has lots of properties that are functions:

var obj = { foo: function() { ... },
            bar: function() { ... },
              ...
          }

then how can you get an array of names of those functions? That is, an array

["foo", "bar", ... ]

thanks.

Answer 1

var names = [];
for( var k in obj ) {
   if(obj.hasOwnProperty(k) && typeof obj[k] == 'function') {
      names.push(k);
   }
}

Answer 2

var functions = [];
for (var prop in obj) {
    if ((typeof obj[prop]) == 'function') {
        // it's a function
        functions.push(prop);
    }
}

Answer 3

Edit: I've slightly misread the question, you want to extract the names of only the properties that are function objects:

function methods(obj) {
  var result = [];
  for (var prop in obj) {
    if (obj.hasOwnProperty(prop) && typeof obj[prop] == 'function') {
      result.push(prop);
    }
  }
  return result;
}

var obj = {
  foo: function() { },
  bar: function() { },
};

methods(obj); // ["foo", "bar"]

I'm using the hasOwnProperty method, to ensure that the enumerated properties in fact exist physically in the object.

Note that this approach and all other answers have a small problem IE.

The JScript's DontEnum Bug , custom properties that shadow non-enumerable properties ( DontEnum ) higher in the prototype chain, are not enumerated using the for-in statement, for example :

var foo = {
  constructor : function() { return 0; },
  toString : function() { return "1"; },
  valueOf : function() { return 2; }
  toLocaleString : function() { return "3"; }
};

for (var propName in foo ) { alert(propName); }

The object foo clearly has defined four own properties, but those properties exist in Object.prototype marked as DontEnum , if you try to enumerate the properties of that object with the for-in statement in IE, it won't find any.

This bug is present on all IE versions, and has been recently fixed in IE9 Platform Preview.

Answer 4

To complete other answers: you can also use instanceof :

var obj = { foo: function() { ... },
            bar: function() { ... },
              ...
          },
    fnArr = [];

for (var label in obj){
  if (obj[label] instanceof Function){
     fnArr.push(label)
  }
}

Answer 5

With ES5 :

var obj = {
    foo: function() {},
    bar: function() {},
    baz: true
};

function getMethods(object) {
    return Object.keys(object).filter(function(key) {
        return typeof object[key] == 'function';
    });
}

getMethods(obj); // [foo, bar]

Object.keys(<object>) returns the names of all enumerable properties of an object as an array, of which the non-functions are filtered out.

Example - works on Chrome release and nightly builds of Webkit and Tracemonkey (Firefox) .