var subscription = web3.eth.subscribe('syncing', function(error, sync){
    if (!error)
        console.log(sync);
})
    .on("data", function(sync){
        console.log(sync);
    })
    .on("changed", function(isSyncing){
        if(isSyncing) {
            console.log("changed");
        } else {
            console.log("changed to false");
        }
    });

geth  --testnet --rpcapi "eth,web3, personal, accounts, miner, admin" --rpccorsdomain='*' --rpc --rpcaddr="0.0.0.0" --rpcport "8545" --ws --wsorigins="*" --wsaddr 0.0.0.0 --fast

let web3 =  new Web3(new Web3.providers.HttpProvider("ws://geth:8546"));

"web3": "^1.0.0-beta.30"