offchain prices

Author: Jayant Krishnamurthy

pyth-aptos-js/README.md

@@ -65,7 +65,7 @@ module example::your_module {
 
     public fun do_something(user: &signer, pyth_update_data: vector<vector<u8>>) {
 
-        // First update the Pyth price feeds
+        // First update the Pyth price feeds. The user pays the fee for the update. 
         let coins = coin::withdraw(user, pyth::get_update_fee());
         pyth::update_price_feeds(pyth_update_data, coins);
 
@@ -85,7 +85,7 @@ We strongly recommend reading our guide which explains [how to work with Pyth pr
 Many applications additionally need to display Pyth prices off-chain, for example, in their frontend application.
 The `AptosPriceServiceConnection` provides two different ways to fetch the current Pyth price.
 The code blocks below assume that the `connection` and `priceIds` objects have been initialized as shown above.
-The first method is a single shot query:
+The first method is a single-shot query:
 
 ```typescript
 // `getLatestPriceFeeds` returns a `PriceFeed` for each price id. It contains all information about a price and has
@@ -104,11 +104,14 @@ This method is useful if you want to show continuously updating real-time prices
 // Subscribe to the price feeds given by `priceId`. The callback will be invoked every time the requested feed
 // gets a price update.
 connection.subscribePriceFeedUpdates(priceIds, (priceFeed) => {
-  console.log("Received a new price feed update!");
-  console.log(priceFeed.getPriceNoOlderThan(60));
+  console.log(`Received update for ${priceFeed.id}: ${priceFeed.getPriceNoOlderThan(60)}`);
 });
-```
 
+// When using the subscription, make sure to close the websocket upon termination to finish the process gracefully.
+setTimeout(() => {
+  connection.closeWebSocket();
+}, 60000);
+```
 
 ### Example
 

pyth-evm-js/README.md

@@ -35,25 +35,6 @@ const priceIds = [
   "0xca80ba6dc32e08d06f1aa886011eed1d77c77be9eb761cc10d72b7d0a2fd57a6", // ETH/USD price id in testnet
 ];
 
-// `getPythLatestPriceFeeds` returns a `PriceFeed` for each price id. It contains all information about a price and has
-// utility functions to get the current and exponentially-weighted moving average price, and other functionality.
-const priceFeeds = connection.getPythLatestPriceFeeds(priceIds);
-// Get the price if it is not older than 60 seconds from the current time.
-console.log(priceFeeds[0].getPriceNoOlderThan(60)); // Price { conf: '1234', expo: -8, price: '12345678' }
-// Get the exponentially-weighted moving average price if it is not older than 60 seconds from the current time.
-console.log(priceFeeds[1].getEmaPriceNoOlderThan(60));
-
-// By subscribing to the price feeds you can get their updates in real-time.
-connection.subscribePriceFeedUpdates(priceIds, (priceFeed) => {
-  console.log("Received a new price feed update!");
-  console.log(priceFeed.getPriceNoOlderThan(60));
-});
-
-// When using subscription, make sure to close the websocket upon termination to finish the process gracefully.
-setTimeout(() => {
-  connection.closeWebSocket();
-}, 60000);
-
 // In order to use Pyth prices in your protocol you need to submit the price update data to Pyth contract in your target
 // chain. `getPriceUpdateData` creates the update data which can be submitted to your contract. Then your contract should
 // call the Pyth Contract with this data.
@@ -104,6 +85,39 @@ contract SomeContract {
 
 We strongly recommend reading our guide which explains [how to work with Pyth price feeds](https://docs.pyth.network/consume-data/best-practices).
 
+### Off-chain prices
+
+Many applications additionally need to display Pyth prices off-chain, for example, in their frontend application.
+The `EvmPriceServiceConnection` provides two different ways to fetch the current Pyth price.
+The code blocks below assume that the `connection` and `priceIds` objects have been initialized as shown above.
+The first method is a single-shot query:
+
+```typescript
+// `getLatestPriceFeeds` returns a `PriceFeed` for each price id. It contains all information about a price and has
+// utility functions to get the current and exponentially-weighted moving average price, and other functionality.
+const priceFeeds = await connection.getLatestPriceFeeds(priceIds);
+// Get the price if it is not older than 60 seconds from the current time.
+console.log(priceFeeds[0].getPriceNoOlderThan(60)); // Price { conf: '1234', expo: -8, price: '12345678' }
+// Get the exponentially-weighted moving average price if it is not older than 60 seconds from the current time.
+console.log(priceFeeds[1].getEmaPriceNoOlderThan(60));
+```
+
+The object also supports a streaming websocket connection that allows you to subscribe to every new price update for a given feed.
+This method is useful if you want to show continuously updating real-time prices in your frontend:
+
+```typescript
+// Subscribe to the price feeds given by `priceId`. The callback will be invoked every time the requested feed
+// gets a price update.
+connection.subscribePriceFeedUpdates(priceIds, (priceFeed) => {
+  console.log(`Received update for ${priceFeed.id}: ${priceFeed.getPriceNoOlderThan(60)}`);
+});
+
+// When using the subscription, make sure to close the websocket upon termination to finish the process gracefully.
+setTimeout(() => {
+  connection.closeWebSocket();
+}, 60000);
+```
+
 ### Examples
 
 There are two examples in [examples](./src/examples/).