To write prototype js

application.js

var mashkar = {

	init: function() {
		this.calculateTotalPrice(); 
	},

	calculateTotalPrice: function() {
		$(document).on("change", '.price-field', function() {
			var variantRow = $(this).closest(".variant-row");
			var sellerPrice = parseFloat($(this).val());
			var basePrice = parseFloat(variantRow.find(".base-price").data("base_price"));
			variantRow.find(".final-price").text((sellerPrice + basePrice).toFixed(2))
		});
	}

};


$(document).ready(function() {
	mashkar.init();
});