Javascript: how to create an instance by class name and an arguments array, like C#?

Question

In C# to create an new instance by name and arguments, we can use reflection as follows:

var instance = Activator.CreateInstance("Com.Account.Person", 
              new object[] { "Jack", 195, 'USA' });

How to do this in Javascript?

var clazzName = document.getElementById('clazzName'); // from an input in the page 
var args = document.getElementById('args').split(','); // from another input in the page
var instance = ....... // how?

See if this helps http://stackoverflow.com/questions/1606797/use-of-apply-with-new-operator-is-this-possible — elclanrs, Feb 23 '14 at 09:07

score 0 · Answer 1 · answered Feb 23 '14 at 09:01

0

You can't. JavaScript does not have classes. It has only objects.

answered Feb 23 '14 at 09:01

stepanian

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score 0 · Accepted Answer · answered Feb 23 '14 at 09:04

0

If you have a factory method of the form:

function MyFactoryMethod() {
  // Perform instantiation here
  return new MyObject();
}

Then you can invoke it, knowing only its name as a string, by doing:

var name = "MyFactoryMethod"
var myObj = window[name]();

That said, I don't endorse this pattern, and I have an inkling that this will get you into tricky situations down the road.

answered Feb 23 '14 at 09:04

Jon Newmuis

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Where is the instantiation ? – Royi Namir Feb 23 '14 at 09:05
Oops, you're right. Changed this to use a factory pattern. – Jon Newmuis Feb 23 '14 at 09:08
@Royi You can't have instantiation because there are no classes. See my answer. This answer will cause confusion to new JavaScript learners. – stepanian Feb 23 '14 at 09:09
Not having classes doesn't mean that the term "instance" is wrong. A class is an object too. – elclanrs Feb 23 '14 at 09:13
@elcanrs A class is not the same thing as an object. The term Instance in JavaScript is confusing, although I agree that it is used. Object is much better. A class is a blueprint. An instance is an object built from that blueprint. JavaScript creates only objects. It cannot create blueprints. – stepanian Feb 23 '14 at 09:18
I guess it depends on the language. An "Object" is more abstract than a "Class". In high level scripting languages a class is typically an object, think Ruby, Python, PHP... – elclanrs Feb 23 '14 at 09:28
@elclanrs In C# and Java, a class is nothing until it is instantiated into an object. Otherwise, it only exists as a blueprint of an object. JavaScript does not have an equivalent. Everything you do in JavaScript creates objects. Even functions are objects. – stepanian Feb 23 '14 at 09:32
@stepanian: Good to know. I'm not familiar with C# or Java. It seems these terms are confusing in general though. It's like trying to explain functions, scopes and closures in JavaScript... – elclanrs Feb 23 '14 at 09:36

score -1 · Answer 3 · answered Feb 23 '14 at 09:07

If you have for ex.

<input id="element" name="elementname" type="text" value="elementvalue" />

and want to get "elementname", "text" and "elementvalue"? You can use this:

var element = document.getElementById('element');
var name = element.name;
var type = element.type;
var value = element.value;

Javascript: how to create an instance by class name and an arguments array, like C#?

3 Answers3