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Use or || to be compatible with FireFox_JavaScript

WBOYOriginal: 2016-05-16 19:29:21922browse

看例子:

运行代码框
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Untitled Document</title> </head> <body> <li> <a href="http://www.blueidea.com/articleimg/bbsimg/smile.gif"/></a> <a href="图片地址">打开</a> </li> <li> <a href="http://www.blueidea.com/articleimg/bbsimg/biggrin.gif"/></a> <a href="图片地址">打开</a> </li> <li> <a href="http://www.blueidea.com/articleimg/bbsimg/confused.gif"/></a> <a href="图片地址">打开</a> </li> </body> </html> <script language="javascript" type="text/javascript"> document.body.onclick = function(evt){ evt = evt || window.event; var o = evt.target || evt.srcElement; window.open(o.previousSibling.href || o.previousSibling.previousSibling.href); return false; } </script>
[Ctrl A 全部选择提示：你可先修改部分代码，再按运行]

找到 document.body.onclick = function(evt),
在IE下,这个evt是不会有的,但是在fireFox下(opera下好像也是)会默认传这个参数.在IE下,这个参数是 null ,想兼容,就这样写.

继续向下：
evt = evt || window.event;
在IE下,evt 就会指向:window.event,在fireFox下,就会指向那个默认参数.
因为在IE下 evt || window.event 相当于: null || window.event,结果还是window.event
而在fireFox下,就相当于 evt || null ,结果就是evt

向下看:
o.previousSibling.href || o.previousSibling.previousSibling.href
前面一个表达式用于IE下,后面一个用于FireFox下.
FireFox下,没有preserveWhiteSpace这个属性,即:把空白也当作一个节点,而IE则默认为false,即把空白不看成一个节点.

这里说到了XMLDom,似乎和上面所说的不相关,但是在FireFox下 previousSibling就是空白,除非两个HTML标签之间没有任何形式的空格.

打开
两个之间有换行(属于空格的一种),所以在FireFox下,取下面一个的前一个节点的话,就必须用:
o.previousSibling.previousSibling.href

可能你还是没有看明白,没关系,再举个简单的:

运行代码框
<script> function test(p1,p2,p3){ p1 = p1 || 100; p2 = p2 || "xlingFairy"; return "p1 = " p1 " p2 = " p2 " p3 = " p3; } alert(test()); alert(test(null,null,"blueidea.com")) </script>
[Ctrl A 全部选择提示：你可先修改部分代码，再按运行]

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