Replace nth occurrence of string

Question

For example:

\'abcjkjokabckjk\'.replace(\'/(abc)/g\',...)

If I want to replace a specify position \'abc\', what I can do?

Like this

Answer 1

Use RegExp constructor to pass variables inside regex.

var s = 'abcjkjokabckjk'
search = 'abc'
var n = 2
alert(s.replace(RegExp("^(?:.*?abc){" + n + "}"), function(x){return x.replace(RegExp(search + "$"), "HHHH")}))

Answer 2

Use Avinash's approach with RegExp constructor

const replace_nth = function (s, f, r, n) {
    // From the given string s, replace f with r of nth occurrence
    return s.replace(RegExp("^(?:.*?" + f + "){" + n + "}"), x => x.replace(RegExp(f + "$"), r));
};

Here's an example outout.

$node
Welcome to Node.js v13.1.0.
Type ".help" for more information.
>
>  const replace_nth = function (s, f, r, n) {
...    // From the given string s, replace f with r of nth occurrence
...    return s.replace(RegExp("^(?:.*?" + f + "){" + n + "}"), x => x.replace(RegExp(f + "$"), r));
...};

> replace_nth('hello world', 'l', 'L', 1)
'heLlo world'

Answer 3

This can be done without RegEx.

String methods String#indexOf, String#lastIndexOf can be used with String#substring

var string = 'abcde|abcde|abcde|abcde',
  needle = 'abc',
  firstIndex = string.indexOf(needle),
  lastIndex = string.lastIndexOf(needle);

// ----------------------------------------------------------------
// Remove first occurence
var first = string.substring(0, firstIndex) + '***' + string.substring(firstIndex + needle.length);
document.getElementById('first').innerHTML = first;

// ----------------------------------------------------------------
// Remove last occurence
var last = string.substring(0, lastIndex) + '***' + string.substring(lastIndex + needle.length);
document.getElementById('last').innerHTML = last;

// ----------------------------------------------------------------
// Remove nth occurence
// For Demo: Remove 2nd occurence
var counter = 2, // zero-based index
  nThIndex = 0;

if (counter > 0) {
  while (counter--) {
    // Get the index of the next occurence
    nThIndex = string.indexOf(needle, nThIndex + needle.length);
  }
  
  // Here `nThIndex` will be the index of the nth occurence
}

var second = string.substring(0, nThIndex) + '***' + string.substring(nThIndex + needle.length);
document.getElementById('second').innerHTML = second;

table tr td:nth-child(2) {
  color: green;
}
td {
  padding: 15px;
}

<table border="1px">
  <tr>
    <td>After replacing <strong>first</strong> occurence:</td>
    <td id="first"></td>
  </tr>
  <tr>
    <td>After replacing <strong>last</strong> occurence:</td>
    <td id="last"></td>
  </tr>
  <tr>
    <td>After replacing <strong>2nd<sup>zero-based index</sup></strong> occurence:</td>
    <td id="second"></td>
  </tr>
</table>