通过点击按钮实现当前网页的下载：

example： downloadAsHtml('test')

const STYLE = 'body{...}' // css样式，保证下载后得到的本地css文件样式不丢失

// ...

/**
 * 将页面已html格式文件下载至本地
 * params name 下载文件名
 **/
function downloadAsHtml (name) {
    let style = document.createElement('style')
    style.type = 'text/css'
    style.innerHTML = STYLE
    document.getElementsByTagName('HEAD').item(0).appendChild(style)
    let htmlPage = document.getElementsByTagName('html')[0].outerHTML
    outputAsHtml(`${name}.html`, htmlPage)
  }

function outputAsHtml (name, data) {
    let urlObject = window.URL || window.webkitURL || window
    let exportBlob = new Blob([data])
    // createElementNS() 方法可创建带有指定命名空间的元素节点
    let saveLink = document.createElementNS('http://www.w3.org/1999/xhtml', 'a')
    saveLink.href = urlObject.createObjectURL(exportBlob)
    saveLink.download = name
    fakeClick(saveLink)
  }

// 伪造点击事件
function fakeClick (obj) {
    let ev = document.createEvent('MouseEvents')
    ev.initMouseEvent('click', true, false, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null)
    obj.dispatchEvent(ev)
  }