无法在 javascript for 循环中读取 null 的属性“长度”
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Cannot read property 'length' of null in javascript for loop
提问by tim peterson
I'm trying to make a markdown editor like Stack Overflow has.
我正在尝试制作一个像 Stack Overflow 一样的 Markdown 编辑器。
I get this error listed in the title if I don't actually type an asterisk AND a http:// containing phrase into the textarea. If I only type an asterisk containing phrase, the error refers to this line: if(linkify.length!==0)
如果我实际上没有在 textarea 中输入星号和包含 http:// 的短语，我会在标题中列出这个错误。如果我只输入一个包含短语的星号，错误是指这一行：if(linkify.length!==0)
Here's a jsfiddleto show you what I mean.
这是一个jsfiddle向您展示我的意思。
Here's my HTML:
这是我的 HTML：
<textarea></textarea>
<div></div><button type="button">Markdownify</button>
Here's my JS:
这是我的JS：
var val=$('textarea').val(), boldify = val.match(/\*\*[A-Za-z0-9]+\*\*/gim),
italicify = val.match(/\*[A-Za-z0-9]+\*/gim),linkify = val.match(/http\:\/\/[A-z0-9]+\.[A-z0-9]+/gim);
$(document.body).on('click', 'button', function() {
val=$('textarea').val(), boldify = val.match(/\*\*[A-Za-z0-9]+\*\*/gim),
italicify = val.match(/\*[A-Za-z0-9]+\*/gim),linkify = val.match(/http\:\/\/[A-z0-9]+\.[A-z0-9]+/gim);
if (boldify.length!== 0){
for (var i=0; i < boldify.length; i++) {
var boldMatch= boldify[i],
boldReplace = boldMatch.replace(/\*\*[A-z0-9]+\*\*/gim, '<span style="font-weight:bold;color:blue;">'+boldMatch+'</span>'),
val = val.replace(boldMatch, boldReplace);
}
val = val.replace(/\*\*/gi, "");
}
if(italicify.length!== 0){
for(var j=0; j < italicify.length; j++){
var italicMatch= italicify[j],
italicReplace = italicMatch.replace(/\*[A-z0-9]+\*/gim, '<span style="font-style:italic;color:red;">'+italicMatch+'</span>');
val = val.replace(italicMatch, italicReplace);
}
val = val.replace(/\*/gi, "");
}
if(linkify.length!== 0){
for(var k=0; k < linkify.length; k++){
var linkMatch= linkify[k],
linkReplace = linkMatch.replace(/http:\/\/[A-z0-9]+\.[A-z0-9]+/gim, '<a href="'+linkMatch+'">'+linkMatch+'</a>');
val = val.replace(linkMatch, linkReplace);
}
}
$('div').html(val);
});
Any help would be greatly appreciated.
任何帮助将不胜感激。
回答by Baz1nga
instead of using matchfunction which returns a null if the string doesnt match the provided regex use the testfunction which returns a true/false and then if you need it you can use the matchfunction.
match如果字符串与提供的正则表达式不匹配test，则不使用返回 null 的函数，而是使用返回 true/false的函数，然后如果需要，可以使用该match函数。
basically you are performing null.lengthwhich is obviously invalid as the matchis returning you a null
基本上你正在执行null.length这显然是无效的，因为它match正在返回一个空值
or you could just perform a nullcheck before you check for the length and just do the regex matching once.
或者您可以null在检查长度之前执行检查，然后只进行一次正则表达式匹配。
if(linkify!==null && linkify.length!== 0)
{
//do smthing
}
回答by jimw
'linkify' is null when there isn't an 'http://' match in the text, so you need to test for that condition:
当文本中没有“http://”匹配时，“linkify”为空，因此您需要测试该条件：
if(linkify && linkify.length)
