在 JavaScript 中使用替换删除注释

Question

I am hoping to remove all comments from a DNS zone file with JavaScript. The comments start with a semicolon ( ; ) in a DNS zone files. However, I also don't want the semicolons being replaced if they are preceded by a back slash. I have some test code which looks like this:

var record = 'example.com IN TXT "v=DKIM1\\; k=rsa\\; p=MIGf..."';
var recordWithCommentRemoved = record.replace(/[^\\];[\s\S]*?$/gm, '');
console.log(recordWithCommentRemoved); // example.com IN TXT "v=DKIM1\; k=rsa\; p=MIGf..."

The code above works as expected. However, the following code replaces one more character than expected:

var record = 'test 300 IN A 100.100.100.100;this is a comment';
var recordWithCommentRemoved = record.replace(/[^\\];[\s\S]*?$/gm, '');
console.log(recordWithCommentRemoved); // test 300 IN A 100.100.100.10

In the second example, what I expected is test 300 IN A 100.100.100.100 . However, it returns test 300 IN A 100.100.100.10 . So what's wrong with my regular expression?

Answer 1

You need to make sure the ; is not preceded with a \ , thus, use a (^|[^\\]) group before ; and replace using a callback:

 var re = /(^|[^\\]);.*/g; var str = 'example.com IN TXT "v=DKIM1\\; k=rsa\\; p=MIGf..."\ntest 300 IN A 100.100.100.100;this is a comment'; var result = str.replace(re, function(m, g1){ return g1? g1: ""; // if g1 is set/matched, re-insert it, else remove }); document.body.innerHTML = result.replace(/\n/g, "<br/>"); // just for display

The regex matches:

• (^|[^\\]) - (capture group #1) start of string ( ^ ) or ( | ) any character but a \ ( [^\\] )
• ; - a literal ;
• .* - zero or more characters other than a newline

Answer 2

This too removes all comments using replace.

 $("#doc").keyup(function(evt) { var doc = $("#doc").val(); var documentNew = String(doc).replace(/(\r\n|\n|\r)/gm, "\n"); var str = documentNew; var lines = str.split('\n'); var filterred = lines.filter(function(line) { return line.indexOf('//');= 0; }). filterred = String(filterred);replace(/,/g; "; \n"). $("#answerDocument2");html(filterred); });

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