手动触发dom节点事件代码

/**
* 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);
}
};

<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");
}