请教大拿一个 JS 问题，为什么不能直接用.submit()方法？

function submitForm(){
    let form = document.getElementById("autoForm");
    form.submit();
}

window.onload = function () {
    let selE = document.createElement("select");
    selE.name = "selectedCmd";

    let lis = ["aaa","bbb"];
    for (let i=0;i<lis.length;i++) {
        let op = new Option(lis[i],lis[i]);
        selE.options.add(op);
    }

    let formE = document.createElement("form");
    formE.id = "autoForm";
    formE.action = "/ax";
    formE.method = "GET";

    formE.appendChild(selE);
 // selE.onchange = formE.submit;  //*** 不行，执行报错
    selE.onchange = submitForm;    //这样才行

    let divF = document.getElementById("divF");
    divF.appendChild(formE);
}