isInstance.js

// Proof of concept only!

function isInstance(value, Type) {
    if (typeof Type.hasInstance === 'function') {
        return Type.hasInstance(value);
    } else {
        return value instanceof Type;
    }
}
isInstance.Primitive = {
    hasInstance: function (value) {
        if (value === null) {
            return true;
        }
        switch(typeof value) {
            case 'undefined':
            case 'boolean':
            case 'number':
            case 'string':
                return true;
            default:
                return false;
        }
    }
};
isInstance.PrimitiveBoolean = {
    hasInstance: function (value) {
        return typeof value === 'boolean';
    }
};
isInstance.PrimitiveNumber = {
    hasInstance: function (value) {
        return typeof value === 'number';
    }
};
isInstance.PrimitiveString = {
    hasInstance: function (value) {
        return typeof value === 'string';
    }
};
isInstance.ValueType = isInstance.Primitive; // for now
isInstance.ReferenceType = {
    hasInstance: function (value) {
        switch(value) {
            case 'array':
                return true;
            case 'object':
                return value !== null;
            default:
                return false;
        }
    }
};