如何为界面的元素添加事件处理？

_scriptOnload = doc.createElement('script').readyState ?
function(node, callback) {
var oldCallback = node.onreadystatechange;
node.onreadystatechange = function() {
var rs = node.readyState;
if (rs === 'loaded' || rs === 'complete') {
node.onreadystatechange = null;
oldCallback && oldCallback();
callback.call(this);
}
};
} :
function(node, callback) {
node.addEventListener('load', callback, false);
};

head = doc.getElementsByTagName('head')[0] || doc.documentElement,
_getScript = function(url, fn) {
var node = doc.createElement('script');
node.src = url;
node.async = true;
_scriptOnload(node, function() {
fn && fn.call(node, '');
if (head && node.parentNode) {
head.removeChild(node);
}
});
head.insertBefore(node, head.firstChild);
return node;
}