feat-issue-123: add rpc url env to replace default rpc url

README.md

@@ -292,3 +292,18 @@ Pro Tips
   * specify which port to run on
 
   * and more!
+
+Env variables
+========
+```text
+NEAR_CLI_MAINNET_RPC_SERVER_URL
+NEAR_CLI_TESTNET_RPC_SERVER_URL
+```
+Clear them in case you want to get back to the default RPC server.
+
+Example:
+
+```shell
+export NEAR_CLI_MAINNET_RPC_SERVER_URL=<put_your_rpc_server_url_here>
+```
+here is a testcase: [jsonrpc.ava.js](./packages/js/__tests__/jsonrpc.ava.js)

packages/js/__tests__/jsonrpc.ava.js

@@ -0,0 +1,10 @@
+import test from "ava";
+import {JsonRpcProvider} from "..";
+
+test("check url", async (t) => {
+  const provider = JsonRpcProvider.fromNetwork("mainnet");
+  if (process.env.NEAR_CLI_MAINNET_RPC_SERVER_URL) {
+    console.log("use rpc",  process.env.NEAR_CLI_MAINNET_RPC_SERVER_URL);
+    t.is(provider.connection.url, process.env.NEAR_CLI_MAINNET_RPC_SERVER_URL.toString());
+  }
+});