code: function bindInvocation (ele, img) {
    // ios iframe 中长按调起
    if (viewer.isIframed && platform.isIOS()) {
      let timeout
      img.addEventListener('touchstart', () => {
        timeout = setTimeout(invoke, 300)
      })
      img.addEventListener('touchmove', () => {
        clearTimeout(timeout)
      })
      img.addEventListener('touchend', () => {
        clearTimeout(timeout)
      })
    }
    // 有 popup 属性的图片点击调起
    if (ele.hasAttribute('popup')) {
      img.addEventListener('click', e => {
        e.stopPropagation()
        invoke()
      })
    }
  
    function invoke () {
      // 图片未加载则不调起
      /* istanbul ignore if */
      if (img.width + img.naturalWidth === 0) {
        return
      }
      let scheme = 'baiduboxapp://v19/utils/previewImage?params=' + encodeURIComponent(JSON.stringify({urls: [img.src]}))
      let iframe = document.createElement('iframe')
      iframe.style.display = 'none'
      iframe.src = scheme
      let body = document.body
      body.appendChild(iframe)
      // 销毁 iframe
      setTimeout(() => {
        body.removeChild(iframe)
        iframe = null
      }, 0)
    }
  }
docs: 调起手百图片浏览器
  应对 popup 不支持缩放，手百 ios iframe 长按无法保存图片的情况
  
  @param  {HTMLElement} ele     mip-img
  @param  {HTMLElement} img     mip-img下的img
  @return {void}         无