将外部HTML加载到包含Javascript的页面中，并在加载时启动JS

var xhr = new XMLHttpRequest();

xhr.open('GET', 'external.html', true);

xhr.onreadystatechange = function() {
  if (xhr.readyState === 4 && xhr.status === 200) {
    // 请求成功完成，可以执行加载的HTML中的Javascript代码
    var response = xhr.responseText;
    var container = document.getElementById('container');
    container.innerHTML = response;
    evalScripts(container);
  }
};

xhr.send();

function evalScripts(container) {
  var scripts = container.getElementsByTagName('script');
  for (var i = 0; i < scripts.length; i++) {
    var script = document.createElement('script');
    script.text = scripts[i].text;
    container.appendChild(script);
  }
}