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$(document).ready( function() {

  					  var el = $('#quantity_wanted');
						  function change( amt ) {

						  	if(el.val() == ''){
						  		var newValue = 1;
						  	}else{
						  		var newValue = parseInt( el.val(), 10 ) + amt;
						  	}

						  	if(newValue > 0){
						  		el.val( newValue );
						  	}

						  }

						  $('#cart_quantity_up').click( function() {
						    change( 1 );
						  } );
						  $('#cart_quantity_down').click( function() {
						    change( -1 );
						  } );
						} );