JavaScript...无法调用未定义的方法匹配
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JavaScript...Cannot call method match of undefined
提问by jared_flack
I'm getting this error: Uncaught TypeError: Cannot call method 'match' of undefinedin my JavaScript. I'm trying to write this without jQuery since it'll be the only js on the site.
我收到此错误：Uncaught TypeError: Cannot call method 'match' of undefined在我的 JavaScript 中。我正在尝试在没有 jQuery 的情况下编写它，因为它将成为网站上唯一的 js。
My code is supposed to add a class, "active", to the <a href="...>in the navigation that links to the current page.
我的代码应该<a href="...>在链接到当前页面的导航中添加一个“活动”类。
I'm guessing it might be the contentLoadedfunction?....source
我猜这可能是contentLoaded功能？....来源
Here's my code...(error occurs on line 9)...fiddle
这是我的代码...（错误发生在第 9 行）...小提琴
(function(window, document, undefined) { contentLoaded(window, function() {
var page = document.location.pathname.match(/[A-z]+$/)[0],
nav_anchors = document.getElementsByTagName('header')[0]
.getElementsByTagName('nav')[0]
.getElementsByTagName('a');
for(i in nav_anchors)
if(nav_anchors[i].href.match(/[A-z]+$/)[0] = page) //LINE 9 <-- Error
nav_anchors[i].classList.add('active');
})
})(this, this.document)
Thanks!
谢谢！
回答by Quentin
NodeListshave length, itemand namedItemproperties.
NodeLists有length,item和namedItem属性。
Use for (var i = 0; i < foo.length; i++)not for i in footo iterate over them and only hit the nodes.
使用for (var i = 0; i < foo.length; i++)notfor i in foo迭代它们，只命中节点。
回答by Salketer
(function(window, document, undefined) { contentLoaded(window, function() {
var page = document.location.pathname.match(/[A-z]+$/)[0],
nav_anchors = document.getElementsByTagName('header')[0]
.getElementsByTagName('nav')[0]
.getElementsByTagName('a');
for(var i=0;i<nav_anchors.length;i++)
if(typeof nav_anchors[i].href != "undefined" && nav_anchors[i].href.match(/[A-z]+$/)[0] == page)
nav_anchors[i].classList.add('active');
})
})(this, this.document)
Added a check if the hrefof the anchor is set, in case you have page anchors without href attributes (Such as <a name="top">called using #top). Added a second =in the IFfor it to work as exepected. And corrected the for syntax.
添加了一个检查是否href设置了锚点，以防您有没有 href 属性的页面锚点（例如<a name="top">使用 #top 调用）。添加第二个=在IF为它工作作为exepected。并更正了 for 语法。
回答by metadings
if(nav_anchors[i].href.match(/[A-z]+$/)[0] = page) //LINE 9 <-- Error
In javaScript the equals sign =is an assignment operator. You probably mean double equals ==where you can check values without type coercion (5 == "5") or triple equals ===for strong typed checks (where 5 !== "5").
在 JavaScript 中，等号=是赋值运算符。您可能指的是双等号==，您可以在没有类型强制的情况下检查值 ( 5 == "5") 或三重等号===进行强类型检查 ( where 5 !== "5")。
回答by Mic
Sometimes document.location.pathname.match(/[A-z]+$/)can be null. If you try to use document.location.pathname.match(/[A-z]+$/)[0]you can not access the 0 Element of null.
有时document.location.pathname.match(/[A-z]+$/)可以为空。如果尝试使用document.location.pathname.match(/[A-z]+$/)[0]则无法访问 null 的 0 元素。
