JavaScript または jQuery を使用して HTML 要素から属性値を抽出するにはどうすればよいですか?

var el = document.getElementById("someId");
for (var i = 0, atts = el.attributes, n = atts.length, arr = []; i < n; i++){
    arr.push(atts[i].nodeName);
}

var nodes=[], values=[];
for (var att, i = 0, atts = el.attributes, n = atts.length; i < n; i++){
    att = atts[i];
    nodes.push(att.nodeName);
    values.push(att.nodeValue);
}

var attrs = $("#someId").prop("attributes");
for (var i = 0; i < attrs.length; i++){
    console.log(attrs[i].nodeName + ": " + attrs[i].value);
}

var content = $("#someId").contents();
for (var i = 0, atts = content.prop("attributes"), n = atts.length, arr = []; i < n; i++){
    arr.push(atts[i].nodeName);
}