The Miller Device - jQuery Plugin

jquery.ba-istype.js

// based on http://zaa.ch/1q

$.isType = function( obj, type ) {
  var opt = Object.prototype.toString,
    result = opt.call( obj ).slice( 8, -1 ).toLowerCase();
  
  if ( type === 'null' || type === 'undefined' ) {
    type = type === 'null' ? opt.call( null ) : opt.call( undefined );
    type = type.slice( 8, -1 ).toLowerCase();
  }
  
  return result === type;
};

/*

// these should all return true

$.isType( {}, 'object' );
$.isType( [], 'array' );
$.isType( 1, 'number' );
$.isType( NaN, 'number' );
$.isType( Infinity, 'number' );
$.isType( function(){}, 'function' );
$.isType( true, 'boolean' );
$.isType( new Date(), 'date' );
$.isType( /omg/, 'regexp' );
$.isType( null, 'null' );
$.isType( undefined, 'undefined' );

*/

This code is needlessly complex and will cause false matches for $.isType(window, 'null'); in current browsers.
I don't agree with the name of the plugin but...

A better approach:

$.isType = function( obj, type ) {
  var result = obj == null ? String( obj ) : {}.toString.call( obj ).slice( 8, -1 ).toLowerCase();
  return result == type;
};

I'm not sure what kind of crack I was smoking at the time, but it seemed important for me to have those extra checks in there. Thanks, JD!