I'm trying to match only words starting with # in javascript, for eg. in the following sample text, only #these should match.

I need to match only words like #these. Ignore the ones like @#this , !#this and in#ignore.

The closer I got is here,

/(\B(#[a-z0-9])\w+)/gi

Ref:

I'm trying to match only words starting with # in javascript, for eg. in the following sample text, only #these should match.

I need to match only words like #these. Ignore the ones like @#this , !#this and in#ignore.

The closer I got is here,

/(\B(#[a-z0-9])\w+)/gi

Ref: https://regex101./r/wU7sQ0/114

• javascript
• regex

• Use a whitespace boundary - /(?:^|\s)(#[a-z0-9]\w+)/g. – Wiktor Stribiżew Commented Aug 3, 2017 at 12:20
• sorry i misread the question, will update this ment – Semi-Friends Commented Aug 3, 2017 at 12:23
• Using whitespace boundary almost works, but I'm wondering if there is something more perfect as I'm using the pattern to search and replace html – shad Commented Aug 3, 2017 at 12:40
• [ ]#these = whitelist (space) or [^@!a-z]#these = blacklist (@, !, a-z) – online Thomas Commented Aug 3, 2017 at 12:41

4 Answers 4

Use a whitespace boundary (?:^|\s):

var rx = /(?:^|\s)(#[a-z0-9]\w*)/gi;
var s = "I need to match only words like #these. \nIgnore the ones like @#this , !#this and in#ignore.";
var m, res=[];
while (m = rx.exec(s)) {
  res.push(m[1]);
}
console.log(res);

Details:

• (?:^|\s) - matches the start of string or whitespace
• (#[a-z0-9]\w*) - Group 1 (m[1]): a #, then an alphanumeric char followed with 0 or more word chars (letters, digits, _ symbols).

See the regex demo, pay attention to what texts are captured, rather to the whole matches.

Or trimming each match:

var rx = /(?:^|\s)(#[a-z0-9]\w*)/gi;
var s = "I need to match only words like #these. \nIgnore the ones like @#this , !#this and in#ignore.";
var results = s.match(rx).map(function(x) {return x.trim();}); // ES5
// var results = s.match(rx).map(x => x.trim()); // ES6
console.log(results);

Why not search start or with space before. see regex / #|^#

I little bit changed your regex to get what do you want.

var p = "I need to match only words like #these. Ignore the ones like @#this , !#this and in#ignore."

[^@!a-z$]\#[a-z]+

That will be match only #these, you can exclude whatever you don't want by adding between first square bracket

you can try this,

txt = "I need to match only words like #these. Ignore the ones like @#this , !#this and in#ignore."

console.log(/(^|\s)(#+\w+)/g.exec(txt))