Given an arbitrary javascript object, how can i fi

Question

I know this is possible in python, but can i get a list of methods for a javascript object?

Answer 1

This function receives an arbitrary object and returns the name of it's prototype, a list with all it's methods and an object with the name of it's properties (and their types). I haven't the opportunity of testing it in a browser, but it works with Nodejs (v0.10.24).

function inspectClass(obj) {    
    var objClass, className;   
    var classProto;
    var methods = [];
    var attributes = {};
    var t, a;
    try {
        if (typeof(obj) != 'function') {
            objClass = obj.constructor;
        } else {
            objClass = obj;      
        }
        className = objClass.name;
        classProto = objClass.prototype        
        Object.getOwnPropertyNames(classProto).forEach(function(m) {
            t = typeof(classProto[m]);
            if (t == 'function') {
                methods.push(m);
            } else {
                attributes[m] = t;
            }       
        });
    } catch (err) {
        className = 'undefined';
    }
    return { 'ClassName' : className,
             'Methods' : methods,
             'Attributes' : attributes
    }
}

Example (with Nodejs):

console.log(inspectClass(new RegExp("hello")));

Output:

{ ClassName: 'RegExp',
  Methods: [ 'constructor', 'exec', 'test', 'toString', 'compile' ],
  Attributes: 
   { source: 'string',
     global: 'boolean',
     ignoreCase: 'boolean',
     multiline: 'boolean',
     lastIndex: 'number' } }

The following examples also work with Nodejs:

console.log(inspectClass(RegExp));
console.log(inspectClass("hello"));
console.log(inspectClass(5));
console.log(inspectClass(undefined));
console.log(inspectClass(NaN));
console.log(inspectClass(inspectClass));

Answer 2

You can loop over the properties in the object and test their type.

for(var prop in whatever) {
    if(typeof whatever[prop] == 'function') {
        //do something
    }
}

Answer 3

To add to the existing answers, ECMAScript 5th ed. provides a way to access all properties of an object (even the non-enumerable ones) using the method Object.getOwnPropertyNames. When trying to enumerate the properties of native objects such as Math, a for..in

for(var property in Math) {
    console.log(property);
}

will print nothing on the console. However,

Object.getOwnPropertyNames(Math)

will return:

["LN10", "PI", "E", "LOG10E", "SQRT2", "LOG2E", "SQRT1_2", "abc", "LN2", "cos", "pow", "log", "tan", "sqrt", "ceil", "asin", "abs", "max", "exp", "atan2", "random", "round", "floor", "acos", "atan", "min", "sin"]

You could write a helper function on top of this that only returns methods given an object.

function getMethods(object) {
    var properties = Object.getOwnPropertyNames(object);
    var methods = properties.filter(function(property) {
        return typeof object[property] == 'function';
    });
    return methods;
}

> getMethods(Math)
["cos", "pow", "log", "tan", "sqrt", "ceil", "asin", "abs", "max", "exp", "atan2", "random", "round", "floor", "acos", "atan", "min", "sin"]

Support for ECMAScript 5th ed. is somewhat bleak at this point, as only Chrome, IE9pre3, and Safari/Firefox nightlies support it.

Answer 4

A single-line solution

Object.getOwnPropertyNames(JSON).filter(function(name){ return 'function' === typeof JSON[name]; })

[ 'parse', 'stringify' ]

Object.getOwnPropertyNames(String).filter(function(name){ return 'function' === typeof String[name]; })

[ 'fromCharCode', 'fromCodePoint', 'raw' ]

Object.getOwnPropertyNames(Array).filter(function(name){ return 'function' === typeof Array[name]; })

[ 'isArray', 'from', 'of' ]