javascript instanceof get type from string name

Question

Let's say I have this (assume the name variable is "receiver"):

if (!(receiver instanceof com.HTMLReceiver)) {
    throw new com.IllegalArgumentException(
        name + " is not an instance of com.HTMLReceiver.");
}

I'd like to factor this code out into a common method so I could call it like this:

Helper.checkInstance(receiver, "com.HTMLReceiver");

But I don't know of a way to convert the com.HTMLReceiver from a string to its actual type so I can use instanceof on it.

Is there a way?

Matthew Flaschen · Accepted Answer · 2010-05-25 04:25:05Z

3

I would call it as:

Helper.checkInstance(receiver, com.HTMLReceiver);

This will not allow you print a type name ("com.HTMLReceiver").

or:

Helper.checkInstance(receiver, com.HTMLReceiver, "com.HTMLReceiver");

You use the user string in the print.

Note that the same type can have multiple type names

var foo = com.HTMLReceiver;

foo and com.HTMLReceiver are names for the same thing.

JavaScript has no way of going from type to type name itself.

If you only pass in the String, I think the only general solution is eval.

edited May 25, 2010 at 4:25

answered May 25, 2010 at 4:04

Matthew Flaschen

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8 Comments

Christian C. Salvadó Over a year ago

Seems that he wants to get the name of the constructor, and concatenate it to the string argument of the exception...

dcp Over a year ago

Cool, that looks promising. But why doesn't it work with "instanceof Number"?

Anurag Over a year ago

Not sure what name refers to, but it looks like it has something to do with receiver.

Matthew Flaschen Over a year ago

It will work with Number. However, number literals are not instances of Number. :) 3 instanceof Number is false, but new Number(3) instanceof Number is true.

Anurag Over a year ago

typeof receiver == 'number'

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