JS error Cannot read properties of undefined (reading ‘length’)

Hi Team

This is the error:

jquery.min.js?ver=3.6.0:2 Uncaught TypeError: Cannot read properties of undefined (reading ‘length’)
at HTMLDocument.<anonymous> (frontend.js?ver=20160615:106)
at e (jquery.min.js?ver=3.6.0:2)
at t (jquery.min.js?ver=3.6.0:2)

I see an uncaught type error, maybe when product is not variable in: asset/js/frontend.js line 106

/*--------------------------------------*/
		  var price_element 	= '',
		  	  
			  variation_id 		= '';
		if( $(".variations_form").attr("data-product_variations").length ){
			var product_attr      = jQuery.parseJSON( $(".variations_form").attr("data-product_variations") );
		}else{
			var product_attr      = '';
		}
		 $('input.variation_id').change( function(){
			
			
			 if( $(smart_variable.__price_update_on).length ){
				 price_element = smart_variable.__price_update_on;
				 
			 }else{
				 price_element = '.' + smart_variable.__price_update_on;
				 
			 }
			
			 if( $(this).parents('li.product').length ){
				
				 price_element   = $(this).parents('li.product').find( price_element );
				 product_attr    =   jQuery.parseJSON( $(this).parents('li.product').find(".variations_form").attr("data-product_variations") );
				 
				 variation_id  =  $(this).parents('li.product').find('input.variation_id').val() ;
				 
			 }else{
				 variation_id   = $('input.variation_id').val(); 
			 }

Can you help me?

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