Question

I have tried to delete an item from a string divided with commas:

var str="this,is,unwanted,a,test";

• if I do a simple str.replace('unwanted',''); I end up with 2 commas
• if I do a more complex str.replace('unwanted','').replace(',,','');
  It might work

But the problem comes when the str is like this:

var str="unwanted,this,is,a,test"; // or "...,unwanted"

However, I could do a ‘if char at [0 or str.length] == comma’, then remove it

But I really think this is not the way to go, it is absurd I need to do 2 replaces and 2 ifs to achieve what I want

I have heard that regex can do powerful stuff, but I simply can’t understand it no matter how hard I try

Important Notes:

• It should match after OR before (not both), or we will end with
  “this,is,,a,test”
• There are no spaces between commas

Answer 1

How about something less flaky than a regex for this sort of replacement?

str = str
     .split(',')
     .filter(function(token) { return token !== 'unwanted' })
     .join(',');

jsFiddle.

However if you are convinced a regex is the best way…

str = str.replace(/(^|,)?unwanted(,|$)?/g, function(all, leading, trailing) {
    return leading && trailing ? ',' : '';
});

(thanks Logan F. Smyth.)

jsFiddle.