Played a bit of code golf with your snippet, but can't figure out how to combine the .map(Number).filter(Number):

    let avgAge = [...document.querySelectorAll('.commtext')]
                  .map(span => parseInt(span.innerText))
                  .map(Number)
                  .filter(Number)
                  .reduce((i,d,c, ages) => ages.reduce((x, y) => x+y) / ages.length)