可视区域的宽高

function client() {
    if (window.innerHTML !== undefined) {
      return {
        "width" : window.innerWidth,
        "height": window.innerHeight
      }
    } else if (document.compatMode === "CSS1Compat") {
      return {
        "width" : document.documentElement.clientWidth,
        "height": document.documentElement.clientHeight
      }
    } else {
      return {
        "width" : document.body.clientWidth,
        "height": document.body.clientHeight
      }
    }
  }