JQuery: Validation image file if file size is too big

HTML+JQUERY : Validation before upload image

//HTML
<p id="error1" style="display:none; color:#FF0000;">
Invalid Image Format! Image Format Must Be JPG, JPEG, PNG or GIF.
</p>
<p id="error2" style="display:none; color:#FF0000;">
Maximum File Size Limit is 4MB.
</p>
<p>
<input type="file" accept="image/*"  name="image_upload_file" id="image_upload_file" required/>
</p>


//jquery
 
	$('#image_upload_file').bind('change', function() {
		if ($('#buttonsubmit').attr('disabled',false)){
			$('#buttonsubmit').attr('disabled',true);
		}
		var ext = $('#image_upload_file').val().split('.').pop().toLowerCase();
		if ($.inArray(ext, ['gif','png','jpg','jpeg']) == -1){
			$('#error1').slideDown("slow");
			$('#error2').slideUp("slow");
			a=0;
		}else{
			
			var picsize = (this.files[0].size);
			if (picsize > 4000000){ // *change size if u want 4000000 = 4MB
				$('#error2').slideDown("slow");
				a=0;
			}else{
				a=1;
				$('#error2').slideUp("slow");
			}
			
			$('#error1').slideUp("slow");
			
			if (a==1){
				$('#buttonsubmit').attr('disabled',false);
        		$('#buttonsubmit').css('color','red'); 
			}
		}
	}); 

#butttonsubmit is defined for which id