Regex – how to match and replace with javascript

Question

I'm trying to match symbol sequence according to these rules:

it's located at the start of the string
case insensitive
it begins with letter V or N
optional space follows
- or – characters follows (only one of them)
optional space follows

Here are example strings that it should match and expression I tried to make using google results :) :

var str = "V - ";
/*var str = "N - ";
var str = "V- ";
var str = "N -";
var str = "N –";
var str = "V– ";*/
str.replace(/^(V|N)\s(-|–)\s/i, 'replaced'); 
alert(str);

However it doesn't seem to work. Can someone help me please and explain how it is used, what I did wrong? Thanks

*it begins with letter V or N* but your regex is expecting `V` or `H`, right? `(V|H|v|h)` — DontVoteMeDown, Nov 19 '14 at 19:14
well right, where's your point? BTW made and edit from `(V|H|v|h)` to `(V|H)` as I discovered `/i` later — simPod, Nov 19 '14 at 19:16
@simPod I think the point is that `N` and `H` are different letters? — Evan Davis, Nov 19 '14 at 19:16
ah damn! I'm learning Russian and sometimes it confuses me :D will make and edit. Thanks! — simPod, Nov 19 '14 at 19:17
Try this regex: `/^[VN] ?[-–] ?/` [or see this demo](http://regex101.com/r/jO9iN2/1) — anubhava, Nov 19 '14 at 19:19
@anubhava that's interesting, I might even prefer yours! Also the link is great — simPod, Nov 19 '14 at 19:24
possible duplicate of [Reference - What does this regex mean?](http://stackoverflow.com/questions/22937618/reference-what-does-this-regex-mean) — Evan Davis, Nov 19 '14 at 19:28

score 2 · Answer 1 · answered Nov 19 '14 at 19:14

2

try this

(V|H|v|h)\s*(-|–)\s*

the \s* gives you the options whitespace

also if you want to find multiple use /g

answered Nov 19 '14 at 19:14

blackmind

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1

You're missing the start-of-string `^`, and you can use `/i` instead of listing both cases. – Evan Davis Nov 19 '14 at 19:18

score 1 · Accepted Answer · answered Nov 19 '14 at 19:16

you are so close. the str.replace function doesn't actually modify str, but it returns a modified copy of it, so what you want is

var str = "V - ";
/*var str = "N - ";
var str = "V- ";
var str = "N -";
var str = "N –";
var str = "V– ";*/
var str2 = str.replace(/^(V|N)\s?(-|–)\s/i, 'replaced'); 
alert(str2);

also, notice the '?' that I added to your expression, that makes the space optional (use * instead for 0 or more spaces)

score 1 · Answer 3 · answered Nov 19 '14 at 19:24

The regex can be simplified:

alert(str.replace(/^[VN]\s*[-–]\s*/i, 'replaced'));

You had expressions like (V|N), but the alternation group is unnecessary when it's single characters. It's equivalent to [VN], which indicates all the possible matches for a single character.

Regex – how to match and replace with javascript

3 Answers3