decordMessage('oppeeennnn','1234');

​

    function decordMessage(m,k) {

        var msg = m.split('');

        var keysplit = k.split('');

        var str ='';

        var j =0

        for (var i=0;i<msg.length;){

            str += msg[i];

            if(j < keysplit.length -2 &&i < keysplit.length && keysplit[j]){

                i = i + parseInt(keysplit[j]);

                j++;

            }

​

            console.log(i +"i")

            console.log(str);

        }

        console.log("after");

        console.log(str);

    }

​