How to ‘undefined’ value and generate alert using jQuery

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JQuery library was developed specifically to simplify and to unify certain JavaScript functionality. However if you need to check a variable against undefined value, there is no need to invent any special method, since JavaScript has a typeof operator, which is simple, fast and cross-platform.

<script type="text/javascript">
	$('#testing_sales').click(function(){
		var testing_fuel_check  = $('.testing_fuel_check').val();
		if(typeof testing_fuel_check === "undefined")
		{
			alert('Please complete Fuel Sales after than complete testing!!');
		}
		else
		{
			
		}
	});
</script>