js-buy-api

example.js

var shopClient = ShopifyBuy.buildClient({
  appId: '',
  apiKey: '',
  myShopifyDomain: ''
});

// Fetching one product
shopClient.fetchProduct(123).then(function(product) {
  // => product
  // product.selectedVariant.checkoutUrl({quantity: 1});
})

// Fetching the products in a collection
shopClient.fetchQueryProducts({collection_id: 123}).then(function(products) {
  // => [products]
});

var cart;
shopClient.createCart().then(function(remoteCart) {
  cart = remoteCart;
});


// once promises are resolved
cart.addVariant({variant: product.selectedVariant, quantity: 1}).then(function(updatedCart) {
  document.location.href = cart.checkoutUrl;
});
// cart.updateLineItem({id: 123, quantity: 307});