Test CORS

test-cors.js

var testEndpointCORS = (url) => {
  var method = "POST";
  var xhr = new XMLHttpRequest();
  var json = {
    jsonrpc: "2.0",
    method: "eth_getBlockByHash",
    params: [
      "0xb3b20624f8f0f86eb50dd04688409e5cea4bd02d700bf6e79e9384d47d6a5a35",
      true,
    ],
    id: 1,
  };
  xhr.onload = console.log;
  xhr.onerror = console.log;
  xhr.open(method, url, true);
  xhr.setRequestHeader("Content-Type", "application/json");
  xhr.send(JSON.stringify(json));
};

How to test:

1. open web console and paste the code above
2. testEndpointCORS(<your_eth_endpoint>)