将HTML转义为实体，将实体转回为HTML

// 将HTML转义为实体
function escape(html){
    var elem = document.createElement('div')
    var txt = document.createTextNode(html)
    elem.appendChild(txt)
    return elem.innerHTML;
}
// 将实体转回为HTML
function unescape(str) {
    var elem = document.createElement('div')
    elem.innerHTML = str
    return elem.innerText || elem.textContent

// 将HTML转义为实体
function escape(html){