在nodejs官网点击下载install,它是怎么判断我的电脑是32位还是64位?

在nodejs官网点击下载install,它是怎么判断我的电脑是32位还是64位的

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用userAgent：

console.log(navigator.userAgent);

在64位Linux下（我的电脑）显示是

Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.120 Safari/537.36

基本上，如果是64位，就会有x86_64或64bit字样。反之则是32位的。

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navigator.userAgent，源码148行请自行查看。

 window._gaq = [['_setAccount', 'UA-10874194-2'], ['_trackPageview']];
  (function(d, t) {
    var g = d.createElement(t),
        s = d.getElementsByTagName(t)[0];
    g.src = '//www.google-analytics.com/ga.js';
    s.parentNode.insertBefore(g, s);
  }(document, 'script'));
  ;(function(d,n) {
    var os = n.platform.match(/(Win|Mac|Linux)/);
    var x = n.userAgent.match(/x86_64|Win64|WOW64/) ||
            n.cpuClass === 'x64' ? 'x64' : 'x86';
    var base = 'http://nodejs.org/dist/v0.10.32/';
    var href = 'node-v0.10.32.tar.gz';
    var db = d.getElementById('downloadbutton');
    var d2;
    switch (os && os[1]) {
      case 'Mac':
        href = 'node-v0.10.32.pkg';
        break;
      case 'Win':
        href = 'node-v0.10.32-' + x + '.msi';
        if (x === 'x64') href = 'x64/' + href;
        break;

      // TODO uncomment when we have these
      // case 'Linux':
      //   // two buttons: .deb and .rpm
      //   href = 'node-v0.10.32-' + x + '.rpm';
      //   var d2 = document.createElement('a');
      //   d2.href = base + 'node-v0.10.32-' + x + '.deb';
      //   d2.className = 'button downloadbutton';
      //   d2.innerHTML = 'INSTALL .deb';
      //   db.innerHTML = 'INSTALL .rpm';
      //   db.parentNode.insertBefore(d2, db);
      //   break;
    }

    db.href = base + href;
    // if there's one download option, then download it at #download
    if (location.hash === '#download' && !d2)
      location.replace(b.href);
  })(document,navigator);