var box = document.getElementsByClassName("textArea-2Spzkt textArea-2Spzkt scrollbarGhostHairline-1mSOM1 scrollbar-3dvm_9")[0];
if(box){
box.addEventListener("keydown", function (e) {
    if (e.keyCode === 13) {
         document.getElementsByClassName("textArea-2Spzkt textArea-2Spzkt scrollbarGhostHairline-1mSOM1 scrollbar-3dvm_9")[0].value = "oh";
    }
});
}