Javascript IE error: 'target' is null or n

问题:

document.onkeydown = function(event) {
    var tagName = event.target.tagName;
    if (tagName != 'INPUT' && tagName != 'TEXTAREA' && !event.alt && event.control) {

        if (event.ctrlKey && event.keyCode == 37) {
            if (_this.currentPage > 1) {
                window.location.href = _this.baseUrl.replace(/%page%/i, _this.currentPage + 1);
            }
        } else if (event.ctrlKey && event.keyCode == 39) {
            if (_this.currentPage < _this.pagesTotal) {
                window.location.href = _this.baseUrl.replace(/%page%/i, _this.currentPage - 1);
            }
        }
    }
}

This gives me an error only in IE 8:

'target' is null or not an object

for that line var tagName = event.target.tagName;

How to fix that. Error happens when I press Ctrl or arrows button.

回答1:

Do it like this:

event = event || window.event;
var tagName = (event.target || event.srcElement).tagName.toUpperCase();

回答2:

IE does not pass in the event object into the event handler. Instead, they use the global event property of the window object. So for IE, you'd use window.event instead.

It is common practice to test for the supplied argument first. You also have to take into account the fact the IE uses srcElement instead of target. To account for all that, use something similar to this:

document.onkeydown = function(event) {
    event = event || window.event;
    var tagName = (event.target || event.srcElement).tagName;
    // Keep up the good work...
}

This should do the trick.