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replaceLast javascript Code Snippet in 2024

stringregexpadvanced

Last Updated: 9 April 2024

Replaces the last occurence of a pattern in a string.

  • Use typeof to determine if pattern is a string or a regular expression.
  • If the pattern is a string, use it as the match.
  • Otherwise, use the RegeExp constructor to create a new regular expression using the RegExp.source of the pattern and adding the 'g' flag to it. Use String.prototype.match() and Array.prototype.slice() to get the last match, if any.
  • Use String.prototype.lastIndexOf() to find the last occurence of the match in the string.
  • If a match is found, use String.prototype.slice() and a template literal to replace the matching substring with the given replacement.
  • If no match is found, return the original string.
const replaceLast = (str, pattern, replacement) => { const match = typeof pattern === 'string' ? pattern : (str.match(new RegExp(pattern.source, 'g')) || []).slice(-1)[0]; if (!match) return str; const last = str.lastIndexOf(match); return last !== -1 ? `${str.slice(0, last)}${replacement}${str.slice(last + match.length)}` : str; };
replaceLast('abcabdef', 'ab', 'gg'); // 'abcggdef' replaceLast('abcabdef', /ab/, 'gg'); // 'abcggdef' replaceLast('abcabdef', 'ad', 'gg'); // 'abcabdef' replaceLast('abcabdef', /ad/, 'gg'); // 'abcabdef'

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