Replace all characters including whitespace in Javascript

Question

I have the following string , s1 , as a part of a longer text (which doesn't have the following patter in it i.e. this pattern only happens once through out the text. The text also includes white spaces and new lines)

<!-- COMPONENTS_LIST_START -->
* [line-vis](line-chart)
* [trend-vis](trend-vis)
<!-- COMPONENTS_LIST_END -->

I want to replace it with the following string , s2 :

<!-- COMPONENTS_LIST_START -->
* [line-vis](line-chart)
* [trend-vis](trend-vis)
* [common-vis](common-vis)
<!-- COMPONENTS_LIST_END -->

I use the following RegEx but it doesn't match it :

str1.replace(/<!-- COMPONENTS_LIST_START -->(\s|.)*<!-- COMPONENTS_LIST_END -->/, str2)

Doesn't this : (\s|.)* mean , all characters including white space characters ?

Also, you probably need the non-greedy quantifier (*?) if your string might have multiple components lists. — p.s.w.g
– p.s.w.g, Commented Apr 27, 2015 at 22:53

Federico Piazza · Accepted Answer · 2015-04-27 23:00:16Z

2

You are using a greedy regex so you will mess things. Btw, you can use [\S\s] ungreedy instead like this:

str1.replace(/<!-- COMPONENTS_LIST_START -->[\S\s]*?<!-- COMPONENTS_LIST_END -->/, str2)

The idea behind [\S\s]*? is to match everything until the first occurrence of your pattern, in your case 

And also as Trott pointed in his answer, assign the string a result:

str1 = str1.replace(/<!-- COMPONENTS_LIST_START -->[\S\s]*?<!-- COMPONENTS_LIST_END -->/, str2);

edited Apr 27, 2015 at 23:00

answered Apr 27, 2015 at 22:52

Federico Piazza

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1 Comment

Shashank Over a year ago

"this pattern only happens once through out the text" so making it non-greedy will only improve performance, not make it "more correct". Also [\S\s] should be written as [^] (the negation of nothing).

Trott · Accepted Answer · 2015-04-27 23:02:45Z

2

Your regular expression works. The problem you are experiencing is that .replace() does not mutate the string. It returns a new string. If you want it to mutate the string, you need to assign the return value.

str1 = str1.replace(/<!-- COMPONENTS_LIST_START -->(\s|.)*<!-- COMPONENTS_LIST_END -->/, str2);

edited Apr 27, 2015 at 23:02

answered Apr 27, 2015 at 22:56

Trott

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4 Comments

Federico Piazza Over a year ago

Actually, OP regex is greedy so technically isn't working, you are using mine :)

Trott Over a year ago

Oh shoot, I accidentally copy/pasted the regexp from your answer thinking I was copy/pasting from his question! Will edit...

Federico Piazza Over a year ago

No worries at all, just wanted to let you know that OP regex wasn't working

Trott Over a year ago

His works, but it replaces the entire string rather than just the inner part. But it appears that's what he wants/expects. Yours is better, though. Leaves the common prefix/suffix intact and all that.

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