[Ethereum] Uncaught TypeError: web3.currentProvider.sendAsync is not a function

You need to provide the address of your geth node to the HttpProvider constructor so your web3 client is connected to a node. Certain web3 functions like contract.at() only works if you are connected to a node. web3.version.api does not need ethereum connection to function.

web3.setProvider(new web3.providers.HttpProvider('http://geth-node-ip:8545'));

If you did set an address for the HttpProvider, then check that the IP and port # are correct. (i'm using 8545 as an example since that's the default RPC port)

You need to instantiate it first. after the npm install web3 in node type :

var web3 = require('web3');

then the console.log(web3) will output

{ [Function: Web3]
  providers: { HttpProvider: [Function], IpcProvider: [Function] } }
undefined

for more info read : https://www.npmjs.com/package/web3