Add replaceLast

snippets/replaceLast.md

@@ -0,0 +1,34 @@
+---
+title: replaceLast
+tags: string,regexp,advanced
+---
+
+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.
+
+```js
+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;
+};
+```
+
+```js
+replaceLast('abcabdef', 'ab', 'gg'); // 'abcggdef'
+replaceLast('abcabdef', /ab/, 'gg'); // 'abcggdef'
+replaceLast('abcabdef', 'ad', 'gg'); // 'abcabdef'
+replaceLast('abcabdef', /ad/, 'gg'); // 'abcabdef'
+```