手动触发dom节点事件代码

在爬代码过程中，碰到一个稀奇古怪的问题。需要手工修改select的值，然后手动触发select的change事件，但使用网络上查到的通过trigger、onchange()事件触发都不执行，没办法，只好继续查找。

还好在stackoverflow网站上看到国外大神的回答，解决了碰到的问题。

原帖地址：http://stackoverflow.com/questions/2490825/how-to-trigger-event-in-javascript

手工触发的代码如下：

/**
 * Fire an event handler to the specified node. Event handlers can detect that the event was fired programatically
 * by testing for a 'synthetic=true' property on the event object
 * @param {HTMLNode} node The node to fire the event handler on.
 * @param {String} eventName The name of the event without the "on" (e.g., "focus")
 */
function fireEvent(node, eventName) {
    // Make sure we use the ownerDocument from the provided node to avoid cross-window problems
    var doc;
    if (node.ownerDocument) {
        doc = node.ownerDocument;
    } else if (node.nodeType == 9){
        // the node may be the document itself, nodeType 9 = DOCUMENT_NODE
        doc = node;
    } else {
        throw new Error("Invalid node passed to fireEvent: " + node.id);
    }

     if (node.dispatchEvent) {
        // Gecko-style approach (now the standard) takes more work
        var eventClass = "";

        // Different events have different event classes.
        // If this switch statement can't map an eventName to an eventClass,
        // the event firing is going to fail.
        switch (eventName) {
            case "click": // Dispatching of 'click' appears to not work correctly in Safari. Use 'mousedown' or 'mouseup' instead.
            case "mousedown":
            case "mouseup":
                eventClass = "MouseEvents";
                break;

            case "focus":
            case "change":
            case "blur":
            case "select":
                eventClass = "HTMLEvents";
                break;

            default:
                throw "fireEvent: Couldn't find an event class for event '" + eventName + "'.";
                break;
        }
        var event = doc.createEvent(eventClass);

        var bubbles = eventName == "change" ? false : true;
        event.initEvent(eventName, bubbles, true); // All events created as bubbling and cancelable.

        event.synthetic = true; // allow detection of synthetic events
        node.dispatchEvent(event, true);
    } else  if (node.fireEvent) {
        // IE-old school style
        var event = doc.createEventObject();
        event.synthetic = true; // allow detection of synthetic events
        node.fireEvent("on" + eventName, event);
    }
};

html代码和调用如下

<a href="http://www.google.com" onclick="alert('clicked')" target="_blank">Go to google</a>
<button>Trigger event</button>

document.getElementsByTagName("button")[0].onclick = function() {
    fireEvent(document.getElementsByTagName("a")[0], "click");
}