I found this regex which validates Instagram usernames

/^(?!.*\.\.)(?!.*\.$)[^\W][\w.]{0,29}$/gim

What I'm trying to do is to replace all characters which not match my regex

let regex = new RegExp(/^(?!.*\.\.)(?!.*\.$)[^\W][\w.]{0,29}$/gim);
const filteredString = replace(text, regex, '');

I tried to add ?! at the start as a negative lookahead but no luck

CodePudding user response：

Instead of using replace you can use match and add all the matches to your filteredString, like shown below:

    let text = `riegiejeyaranchen
riegie.jeyaranchen
_riegie.jeyaranchen
.riegie
riegie..jeyaranchen
riegie._.jeyaranchen
riegie.
riegie.__`;
    let regex = new RegExp(/^(?!.*\.\.)(?!.*\.$)[^\W][\w.]{0,29}$/gim);
    let filteredString = '';
    text.match(regex).forEach(value =>
    {
        filteredString  = value   '\r\n';
    });
    console.log(filteredString);

Of course the \r\n is optional (just places one on each line).

Now you get a string containing non matches.

CodePudding user response：

Based on the regex /^(?!.*\.\.)(?!.*\.$)[^\W][\w.]{0,29}$/, the name must not have consecutive dots, no leading and trailing dots, and have max 30 word/dot chars. This code cleans up names accordingly:

[
  'f',
  'foobar',
  '_foo.bar',
  '_foo..bar',
  '_foo...bar',
  '_foo.bar.',
  '.foo.bar',
  'foo<$^*>bar',
  '123456789012345678901234567890',
  '1234567890123456789012345678901'
].forEach(name => {
  let clean = name
    .replace(/\.{2,}/g, '.')  // reduce multiple dots to one dot
    .replace(/^\. /, '')      // remove leading dots
    .replace(/\. $/, '')      // remove trailing dots
    .replace(/[^\w\.]/g, '')  // remove non word/dot chars
    .replace(/^(.{30}). /, '$1'); // restrict to 30 chars
  console.log(name   ' => '   clean);
});

Output:

f => f
foobar => foobar
_foo.bar => _foo.bar
_foo..bar => _foo.bar
_foo...bar => _foo.bar
_foo.bar. => _foo.bar
.foo.bar => foo.bar
foo<$^*>bar => foobar
123456789012345678901234567890 => 123456789012345678901234567890
1234567890123456789012345678901 => 123456789012345678901234567890

Note that the original regex requires at least one char. You need to test for empty string after cleanup.