<html><head><meta charset="UTF-8"><title>Ethereum test</title><script>function testCallback(err, res){console.log('@@@ testCallback err:'+err+' res:'+res);}function test(){console.log('@@@ test');web3.eth.subscribe('newBlockHeaders', testCallback);console.log('@@@ test done');}</script></head><body><h1>Ethereum test</h1><button onclick="test()" type="button">test()</button><div id="result">...</div></body></html>