86 lines
2.7 KiB
Markdown
86 lines
2.7 KiB
Markdown
---
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id: 587d7dbb367417b2b2512bab
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title: Use Capture Groups to Search and Replace
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challengeType: 1
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forumTopicId: 301368
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---
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## Description
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<section id='description'>
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Searching is useful. However, you can make searching even more powerful when it also changes (or replaces) the text you match.
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You can search and replace text in a string using <code>.replace()</code> on a string. The inputs for <code>.replace()</code> is first the regex pattern you want to search for. The second parameter is the string to replace the match or a function to do something.
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```js
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let wrongText = "The sky is silver.";
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let silverRegex = /silver/;
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wrongText.replace(silverRegex, "blue");
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// Returns "The sky is blue."
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```
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You can also access capture groups in the replacement string with dollar signs (<code>$</code>).
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```js
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"Code Camp".replace(/(\w+)\s(\w+)/, '$2 $1');
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// Returns "Camp Code"
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```
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</section>
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## Instructions
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<section id='instructions'>
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Write a regex <code>fixRegex</code> using three capture groups that will search for each word in the string "one two three". Then update the <code>replaceText</code> variable to replace "one two three" with the string "three two one" and assign the result to the <code>result</code> variable. Make sure you are utilizing capture groups in the replacement string using the dollar sign (<code>$</code>) syntax.
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</section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- text: You should use <code>.replace()</code> to search and replace.
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testString: assert(code.match(/\.replace\(.*\)/));
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- text: Your regex should change <code>"one two three"</code> to <code>"three two one"</code>
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testString: assert(result === "three two one");
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- text: You should not change the last line.
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testString: assert(code.match(/result\s*=\s*str\.replace\(.*?\)/));
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- text: <code>fixRegex</code> should use at least three capture groups.
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testString: assert((new RegExp(fixRegex.source + '|')).exec('').length - 1 >= 3);
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- text: <code>replaceText</code> should use parenthesized submatch string(s) (i.e. the nth parenthesized submatch string, $n, corresponds to the nth capture group).
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testString: '{
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const re = /(\$\d{1,2})+(?:[\D]|\b)/g;
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assert(replaceText.match(re).length >= 3);
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}'
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='js-seed'>
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```js
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let str = "one two three";
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let fixRegex = /change/; // Change this line
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let replaceText = ""; // Change this line
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let result = str.replace(fixRegex, replaceText);
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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let str = "one two three";
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let fixRegex = /(\w+) (\w+) (\w+)/g; // Change this line
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let replaceText = "$3 $2 $1"; // Change this line
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let result = str.replace(fixRegex, replaceText);
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```
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</section>
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