Facebook 如何在加载不同页面时保持页眉和页脚固定?

To make this happen with Javascript, all you have to do is assign a click event handler to those links like so...

var header = document.getElementById('header');
var headerLinks = header.getElementsByTagName('a');

for(var i = 0, l = headerLinks.length; i < l; i++) {
  headerLinks[i].onclick = function() {
    var href = this.href;

    //Load the AJAX page (this is a whole other topic)
    loadPage(href);  

    //Update the address bar to make it look like you were redirected
    location.hash = '#' + href;

    //Unfocus the link to make it look like you were redirected
    this.blur();

    //Prevent the natural HTTP redirect
    return false;
  }
}

这种方法的一个绝妙的好处是它允许后退按钮发挥作用(添加了一些技巧)，这在传统上一直是长期使用 AJAX 的痛苦副作用.我不能 100% 确定这个诡计是什么，但我敢打赌，它能够以某种方式检测浏览器何时修改片段标识符(可能每 500 毫秒检查一次).