I'm a bit of a javascript noob, but I have a general question that has been bothering me. Lets take an example:

If I hop into a JS console on Chrome, I can easily browse the window object. window seems to list a lot 'class types', so to speak. For example, window.CSSPrimitiveValue is one such property. When I evaluate window.CSSPrimitiveValue in the console, I get back what looks like a constructor (possibly):

function CSSPrimitiveValue() { [native code] }

So it looks like the function was implemented in some native language. No matter. Naturally, I want to construct one of these things, like so:

var test = new CSSPrimitiveValue();

But then I get an error:

TypeError: Illegal constructor

I suspect that either I am calling the constructor incorrectly, or it isn't a constructor at all. I'm a pretty big JS noob about this, but is there any way for me to manually construct one of these objects? What would be the method to going about that?

I'm a bit of a javascript noob, but I have a general question that has been bothering me. Lets take an example:

If I hop into a JS console on Chrome, I can easily browse the window object. window seems to list a lot 'class types', so to speak. For example, window.CSSPrimitiveValue is one such property. When I evaluate window.CSSPrimitiveValue in the console, I get back what looks like a constructor (possibly):

function CSSPrimitiveValue() { [native code] }

So it looks like the function was implemented in some native language. No matter. Naturally, I want to construct one of these things, like so:

var test = new CSSPrimitiveValue();

But then I get an error:

TypeError: Illegal constructor

I suspect that either I am calling the constructor incorrectly, or it isn't a constructor at all. I'm a pretty big JS noob about this, but is there any way for me to manually construct one of these objects? What would be the method to going about that?

• javascript

• In some cases I was able to create my own object that has the same properties and methods as the object I wasn't allowed to create and it worked. – The Muffin Man Commented Nov 4, 2016 at 19:41

1 Answer 1

Any function that is written in JavaScript can be a constructor when called using the new keyword. As you already noticed the function you are dealing with is native, i.e. written in C or C++ (probably C++ since Chrome's JavaScript engine is written in C++, too). Native functions/objects can have specific behaviour such as your case where you cannot use it as a constructor - there's nothing you can do.

That "function" doesn't even have a .call() method, you you also cannot call it on an object you created before (not that it would be very useful as it wouldn't have the proper [[Prototype]] set)