https://ervinlaszlobooks.com/webassist/plugins/shopping_cart/change_option.js

1//product
2
3var clickAnchor = -1;
4
5initGallery =  function() {
6    if ($$(".pg-sd-thumbnails").length > 0) {
7      var allAnchors = $$(".pg-sd-thumbnails")[0].getElements('a');
8      if (allAnchors.length > 0) allAnchors[0].fireEvent('click');
9	}
10	if (clickAnchor != -1) {
11	  setTimeout("clickAnchor.fireEvent('click')",500);
12	}
13}
14
15function updateProductInit() {
16  updateProduct(true);	
17}
18
19updateProduct = function(initial) {	
20	var form = document.id('atc-form');
21	var productID = document.id('product-id').get('value');
22	var groupingID = document.id('product-grouping-id').get('value');
23	var requestPath = document.id('product-path').get('value');
24	var imagesFolder = document.id('product-images-folder').get('value');
25	var optionsArray = [];
26	//get options
27	var hasoptions = false;
28	form.getElements('select').each(function(select) {
29		if(select.hasClass('product-option') && !select.hasClass('issimple')) {
30			hasoptions = true;
31			optionsArray.push(select.get('value'));
32		}
33	});
34    if (!hasoptions) return;
35	
36	//reset errors
37	document.id('add-fields').setStyle('display', 'none');
38	document.id('not-sold').setStyle('display', 'none');
39	document.id('sold-out').setStyle('display', 'none');
40	
41	//loading...
42	document.id('checking-availability').setStyle('display', 'block');
43	form.getElements('input,select').set('disabled', true);
44	
45	optionsArray.sort(function(a, b) {
46		return a - b;
47	});
48	
49	//call
50	clickAnchor = -1;
51	new Request.JSON({
52		url: requestPath,
53		method: 'post',
54		onSuccess: function(product) {
55			//document.id('ProductName').set('html', product.ProductName);
56			//document.id('ProductImage').set('src', product.ProductImage);
57			if (product.ProductImage != "") {
58				if ($$(".pg-sd-thumbnails").length > 0) {
59					var allAnchors = $$(".pg-sd-thumbnails")[0].getElements('a');
60					for (var x=0; x<allAnchors.length; x++) {
61					  if (allAnchors[x].getElement('img').get("src") == product.ProductImage) {
62						clickAnchor = allAnchors[x];
63						startSlide = x;
64	                    if (!initial) clickAnchor.fireEvent('click');
65					  }
66					}
67					if (clickAnchor == -1) {
68						allAnchors[0].fireEvent('click');
69					}
70				}
71			} else {
72				if ($$(".pg-sd-thumbnails").length > 0) {
73					var allAnchors = $$(".pg-sd-thumbnails")[0].getElements('a');
74					allAnchors[0].fireEvent('click');
75				}
76			}
77			document.id('ProductPrice').set('html', product.ProductPrice);
78			document.id('ProductSalePrice').set('html', product.ProductSalePrice);
79			if (product.ProductPrice != product.ProductSalePrice) {
80				document.id("details-sale-price").setStyle('display', 'block');
81				document.id("details-orig-price").setStyle('text-decoration', 'line-through');
82			} else {
83				document.id("details-sale-price").setStyle('display', 'none');
84				document.id("details-orig-price").setStyle('text-decoration', 'none');
85			}
86			/*
87			//retail price
88			if(parseFloat(product.ProductPrice) < parseFloat(product.ProductRetailPrice)) {
89				document.id('ProductRetailPrice').set('html', product.ProductRetailPrice);
90				document.id('ProductRetailPriceSave').set('html', (product.ProductRetailPrice - product.ProductPrice).toFixed(2));
91				document.id('retail-price-row').setStyle('display', 'block');
92			}
93			else {
94				document.id('retail-price-row').setStyle('display', 'none');
95			}
96			*/
97			
98			//set long description only for the default product
99			if(product.ProductLongDesc) {
100				if (document.id('ProductLongDesc')) document.id('ProductLongDesc').set('html', product.ProductLongDesc);
101			}
102			
103			if(product.ProductSKU) {
104			  if (document.id('the_sku')) document.id('the_sku').set('html',product.ProductSKU);
105			}
106			
107			if(document.id('WA_Store_Cart_1_ID_Add')) document.id('WA_Store_Cart_1_ID_Add').set('value', product.ProductID);
108			document.id('product-id').set('value', product.ProductID);
109			
110			//stock messages
111			if((product.ProductStock > 0 || product.ProductUnlimited == 1) && product.ProductLive == 1) {
112				document.id('add-fields').setStyle('display', 'block');
113			}
114			if(product.ProductLive == 0) {
115				document.id('not-sold').setStyle('display', 'block');
116			}
117			if(product.ProductStock <= 0 && product.ProductLive == 1 && product.ProductUnlimited == 0) {
118				document.id('sold-out').setStyle('display', 'block');
119			}
120			
121			//done loading
122			document.id('checking-availability').setStyle('display', 'none');
123			form.getElements('input,select').set('disabled', false);
124		}
125	}).send(Hash.toQueryString({
126		'grouping_id': groupingID,
127		'options': optionsArray.join(',')
128	}));
129};