Initial version of js sdk for express relay (#1281)

express_relay/sdk/js/.eslintrc.js

@@ -0,0 +1,6 @@
+module.exports = {
+  root: true,
+  parser: "@typescript-eslint/parser",
+  plugins: ["@typescript-eslint"],
+  extends: ["eslint:recommended", "plugin:@typescript-eslint/recommended"],
+};

express_relay/sdk/js/.gitignore

@@ -0,0 +1 @@
+lib/

express_relay/sdk/js/README.md

@@ -0,0 +1,74 @@
+# Pyth Express Relay JS SDK
+
+Utility library for interacting with the Pyth Express Relay API.
+
+## Installation
+
+### npm
+
+```
+$ npm install --save @pythnetwork/express-relay-evm-js
+```
+
+### Yarn
+
+```
+$ yarn add @pythnetwork/express-relay-evm-js
+```
+
+## Development
+
+To generate the latest type declarations from the server openapi schema, run:
+
+```bash
+npm run generate-api-types
+```
+
+## Quickstart
+
+```typescript
+import {
+  Client,
+  OpportunityParams,
+  BidInfo,
+} from "@pythnetwork/express-relay-evm-js";
+
+const client = new Client({ baseUrl: "https://per-staging.dourolabs.app/" });
+
+function calculateOpportunityBid(
+  opportunity: OpportunityParams
+): BidInfo | null {
+  // searcher implementation here
+  // if the opportunity is not suitable for the searcher, return null
+}
+const opportunities = await client.getOpportunities();
+
+for (const opportunity of opportunities) {
+  const bidInfo = calculateOpportunityBid(order);
+  if (bidInfo === null) continue;
+  const opportunityBid = await client.signOpportunityBid(
+    opportunity,
+    bidInfo,
+    privateKey // searcher private key with appropriate permissions and assets
+  );
+  await client.submitOpportunityBid(opportunityBid);
+}
+```
+
+### Example
+
+There is an example searcher in [examples](./src/examples/) directory.
+
+#### SimpleSearcher
+
+[This example](./src/examples/SimpleSearcher.ts) fetches `OpportunityParams` from the specified endpoint,
+creates a fixed bid on each opportunity and signs them with the provided private key, and finally submits them back to the server. You can run it with
+`npm run simple-searcher`. A full command looks like this:
+
+```bash
+npm run simple-searcher -- \
+  --endpoint https://per-staging.dourolabs.app/ \
+  --bid 100000 \
+  --chain-id op_sepolia \
+  --private-key <YOUR-PRIVATE-KEY>
+```