I know this is possible in python, but can i get a list of methods for a javascript object?
4 Answers
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
}
}
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.
3 Comments
Christian C. Salvadó
+1, I don't see any reason for a downvote. BTW, IE9pre3 also supports it.
Anurag
thanks @CMS, it's good to see IE on its toes with v9. Updated answer.
Christian C. Salvadó
yes, I'm really happy to see IE9 going in a good path, I've found only a few bugs (8+) regarding property descriptors and
Object.create, hope this weekend I get some time to report them. :)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));
Comments
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' ]
