function parseXml(xml) {
  //跨浏览器处理 XML
  var xmldom = null

  if (typeof DOMParser != "undefined") {
    xmldom = new DOMParser().parseFromString(xml, "text/xml")
    var errors = xmldom.getElementsByTagName("parsererror")
    if (errors.length) {
      throw new Error("XML parsing error:" + errors[0].textContent)
    }
  } else if (typeof ActiveXObject != "undefined") {
    xmldom = createDocument()
    xmldom.loadXML(xml)
    if (xmldom.parseError != 0) {
      throw new Error("XML parsing error:" + xmldom.parseError.reason)
    }
  } else {
    throw new Error("No XML parser available.")
  }
  return xmldom
}

//序列化 xmldom 文档
function serializeXML(xmldom) {
  if (typeof XMLSerializer != "undefined") {
    //兼容 ie9+ safari Chrome opera
    var serializer = new XMLSerializer()
    return serializer.serializeToString(xmldom)
  } else if (typeof xmldom.xml != undefined) {
    //兼容 ie9.0 以下
    return xmldom.xml
  } else {
    throw new Error("serialize XML Dom failed!")
  }
}

var iNum1 = 25 //25 等于 00000000000000000000000000011001
var iNum2 = ~iNum1 //转换为 11111111111111111111111111100110
alert(iNum2) //输出 "-26"

//单个 ~
console.log(~1337) // -1338
//数字输入
console.log(~~47.11) //47
console.log(~~1.9999) //1
console.log(~~3) //3

console.log(~~[]) //0
console.log(~~NaN) //0
console.log(~~null) //0

// | 0 也是相同的效果
console.log([] | 0) //0
console.log(NaN | 0) //0
console.log(null | 0) //0