问是否有一个等价的elem.innerHTML来获取标记体中的代码？

EN

HTMLElement.prototype.tagHTML = function(){
    // we create a clone to avoid doing anything to the original:
    var clone = this.cloneNode(),
    // creating a regex, using new RegExp, in order to create it
    // dynamically, and inserting the node's tagName:
        re = new RegExp('<' + this.tagName + '\\s+','i'),
    // 'empty' variables for later:
        closure, str;

    // removing all the child-nodes of the clone (we only want the
    // contents of the Node's opening HTML tag, so remove everything else):
    while (clone.firstChild){
        clone.removeChild(clone.firstChild);
    }

    // we get the outerHTML of the Node as a string,
    // remove the opening '<' and the tagName and a following space,
    // using the above regular expression:
    str = clone.outerHTML.replace(re,'');

    // naively determining whether the element is void
    // (ends with '/>') or not (ends with '>'):
    closure = str.indexOf('/>') > -1 ? '/>' : '>';

    // we get the string of HTML from the beginning until the closing
    // string we assumed just now, and then trim any leading/trailing
    // white-space using trim(). And, of course, we return that string:
    return str.substring(0,str.indexOf(closure)).trim();
};

console.log(document.getElementById('test').tagHTML());
console.log(document.getElementById('demo').tagHTML());