How to extract a string with RegExp in JavaScript?

Question

I want extract an Id from the string <p>id = 22<p>\\n<p>1. iteration, 1. task<p> <p>id = 22<p>\\n<p>1. iteration, 1. task<p>

with:

var str="<p>id = 22<p>\n<p>1. iteration, 1. task<p>";
var patt1=/<p>id = (.*)<p>/;
document.write(str.match(patt1));

but somehow it returns to the browser:

id = 22 
,22

Why so? Why 2 matches?

Answer 1

() is a grouping operator useful for extracting portions of the match. If you just want to extract the id then use str.match(patt1)[1]

Answer 2

/<p>id[^<]+<p>/

Seems to be a better fit for your task. But your input string is very confusing. Shouldn't it be some HTML open-closed tags sequence?