Javascript function for checking a variables type or empty/unset variables - similar to PHP's empty()

I've been building on this one all week and I'm finding it more and more useful for quickly writing variable checks at the top of functions. You can use it to easily check if a var is defined or check if it is of a certain type. It's a work in progress but it's very handy. Check out the commented examples to get an idea of potential uses. Ideas for improvements/additions are welcome!

Please see note before copying my code>>

//CHECK TYPE OF PASSED OBJ:
function is(obj,type){
 switch(type){
  case 'array': case 'ar': //ARRAY:
   return(String(obj.constructor).indexOf('Array')>-1)
  break;
  case 'integer': case 'int': case 'number': //NUMBER:
   return((parseFloat(obj) == parseInt(obj)) && !isNaN(obj))
  break;
  default: //IS EMPTY:
   if(obj==null || obj==undefined || obj==' ' || obj==0 || obj==false || obj=="false" || obj=='' || obj=="\n") return(false);
   return(true)
 }
}
/*EXAMPLES:
returns true if myvar is a positive value (string, number, array, DOM element, etc):
if(is(myvar)){..continue with function...}

returns true if myvar is an array:
if(is(myvar,'array')){..continue with function...}

returns true if myvar is an integer or can be converted to an integer:
if(is(myvar,'int')){..continue with function...}
*/


//CHECKS IF ANY OF THE PASSED ARG(S) ARE BLANK OR FALSE OR 0 OR UNDEFINED:
function isempty(){
 for (var i = 0; i < arguments.length; i++) {
  if(!is(arguments[i])){return(true)}
 }  
 return(false)
}
/*EXAMPLE:
if(isempty(requiredVar1,requiredVar2,requiredVar3)){
       return(false);
}else{...continue with function...}
*/