[Ethereum] How to make synchronous web3.js function calls

go-ethereumweb3js

I am using the web3.js library directly in HTML, not via Node.js to interact with my local geth node. The following code gives me an error (web3.min.js:2 Uncaught TypeError: e is not a function) when running in a minimal test website in Chrome: 

document.getElementById("output").innerText = "block number: " + web3.eth.getBlockNumber();

Instead, I have to go via an asynchronous call:

web3.eth.getBlockNumber(function(err, res){document.getElementById("output").innerText = "block number: " + res; });

Is there no way to make this call synchronous? I know that it does work synchronously in the geth JS console, why is this different when using via web3.js in a browser? This is especially confusing since the wiki states:

As this API is designed to work with a local RPC node, all its functions use synchronous HTTP requests by default.

Just for completion here my complete page:

<html>
  <head>
    <!-- you can also download web3.min.js, this example is optimized for minimal effort -->
    <script type="text/javascript" src="http://rawgit.com/ethereum/web3.js/master/dist/web3.min.js"></script>
  </head>
  <body>
    <div id="output">default</div>
    <script>
      var nodeUrl = "http://localhost:8545";
      var web3 = new Web3(new Web3.providers.HttpProvider(nodeUrl));
      web3.eth.getBlockNumber(function(err, res){document.getElementById("output").innerText = "block number: " + res; });
      //document.getElementById("output").innerText = "block number: " + web3.eth.getBlockNumber(); // not working
    </script>
  </body>
</html>

Best Answer

You have to use web3.eth.blockNumber: it's a property, not a function.

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