JS Promise Trouble

function async(generator) { 
    let promices = generator(); 
    let pr = Promise.resolve(); 
 
    function f() { 
         
        let currentGenObject = promices.next(); 
 
        while (!(currentGenObject.done)) { 
            pr = pr.then((result) => { 
                currentGenObject = promices.next(result); 
                return currentGenObject.value; 
            }); 
        } 
    } 
    return pr.then(f); 
}