function getIndexFromDomOrSelector(domOrSelector){
    let dom;
    // 檢查是dom還是Selector
    if(domOrSelector instanceof HTMLElement || domOrSelector instanceof Element){
        dom = domOrSelector;
    }else if(typeof domOrSelector === "string"){
        dom = document.querySelector(domOrSelector);
        if(!dom) throw new Error("selector無(wú)效，找不到dom")
    }else{
        throw new Error("參數(shù)不合法");
    }
    // 獲取所有的兄弟節(jié)點(diǎn)
    const brothers = Array.from(dom.parentNode.children);

    return brothers.indexOf(dom);
}

// 方式1
getIndexFromDomOrSelector("#a")
// 方式2
const td = document.getElementById("a");
getIndexFromDomOrSelector(td)

function searchIndex(id){
    //獲取 td
    var td = document.getElementById("td");
    //獲取所有的 td
    var arr = Array.from(td.parentNode.children);

    //遍歷
    arr = arr.filter(function(item){
        return td == item;
    });
}