partial.js

function partial(fn /*, rest args */){
  const newArgs = Array.apply(null, arguments).slice(1);
  return function(){
    const fnArgs = newArgs.concat(Array.apply(null, arguments));
    fn.apply(null, fnArgs);  
  }
}

const Logger = {
  log(level, dateFormat, msg) {
    console.log(level, dateFormat, msg);
  }
};

const info = partial(Logger.log, "info", "ISO8601");
info("Application started");