39 lines
1.5 KiB
Markdown
39 lines
1.5 KiB
Markdown
---
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title: Replace last occurrence in string
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tags: string,regexp
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author: chalarangelo
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cover: waves
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firstSeen: 2021-04-22T09:01:22+03:00
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lastUpdated: 2021-04-22T09:01:22+03:00
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---
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Replaces the last occurrence of a pattern in a string.
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- Use `typeof` to determine if `pattern` is a string or a regular expression.
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- If the `pattern` is a string, use it as the `match`.
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- Otherwise, use the `RegExp` constructor to create a new regular expression using the `RegExp.prototype.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.
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- Use `String.prototype.lastIndexOf()` to find the last occurrence of the match in the string.
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- If a match is found, use `String.prototype.slice()` and a template literal to replace the matching substring with the given `replacement`.
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- If no match is found, return the original string.
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```js
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const replaceLast = (str, pattern, replacement) => {
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const match =
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typeof pattern === 'string'
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? pattern
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: (str.match(new RegExp(pattern.source, 'g')) || []).slice(-1)[0];
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if (!match) return str;
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const last = str.lastIndexOf(match);
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return last !== -1
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? `${str.slice(0, last)}${replacement}${str.slice(last + match.length)}`
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: str;
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};
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```
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```js
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replaceLast('abcabdef', 'ab', 'gg'); // 'abcggdef'
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replaceLast('abcabdef', /ab/, 'gg'); // 'abcggdef'
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replaceLast('abcabdef', 'ad', 'gg'); // 'abcabdef'
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replaceLast('abcabdef', /ad/, 'gg'); // 'abcabdef'
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```
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