javascript - Why is this regular expression so slow? -

i trying trim leading , trailing whitespace , newlines string. newlines written \n (two separate characters, slash , n). in other words, string literal, not cr lf special character.

for example, this:

\n \nright after valid newline:\nand here second line. \n

should become this:

right after valid newline:\nand here second line.

i came solution:

text = text         .replace(/^(\s*(\\n)*)*/, '') // beginning         .replace(/(\s*(\\n)*)*$/, '') // end 

these patterns match fine according regexpal.

however, second pattern (matching end of string) takes long time — 32 seconds in chrome on string couple of paragraphs , few trailing spaces. first pattern quite fast (milliseconds) on same string.

here codepen demonstrate it.

why slow? there better way go this?

the reason takes long because have * quantifying 2 more *

a explanation can found in php manual, don't think javascript supports once-only subpatterns.

i suggest regex instead:

text = text.replace(/^(?:\s|\\n)+|(?:\s|\\n)+$/g,"");