动态加script

loadScript

function loadScript(url, attributesParam, optsParam) {
  var attributes = attributesParam || {};
  // optional
  var opts = optsParam || {};

  var script = document.createElement('script');
  // default value
  if (attributes.defer === undefined) {
    attributes.defer = true;
  }
  if (opts.async === undefined) {
    attributes.async = true;
  }
  // optional attribute
  for (var attributeKey in attributes) {
    script.setAttribute(attributeKey, attributes[attributeKey]);
  }

  // load url
  script.src = url;

  // callback
  script.onload = function() {
    if (opts.onload) opts.onload();
  };
  script.onerror = function() {
    if (opts.onerror) opts.onerror();
  };
  // load script
  var _loadScript = function() {
    if (opts.appendBody) {
      var body = document.getElementsByTagName('body')[0];
      body.appendChild(script);
    }
    else {
      var lastScript = document.getElementsByTagName('script')[0];
      lastScript.parentNode.insertBefore(script, lastScript);
    }
  };
  // timeout support
  if (opts.timeout) {
    setTimeout(function() {
        _loadScript();
    }, opts.timeout);
  }
  else {
    _loadScript();
  }
}