freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/regular-expressions/use-capture-groups-to-search-and-replace.english.md

id, title, challengeType, forumTopicId

id	title	challengeType	forumTopicId
587d7dbb367417b2b2512bab	Use Capture Groups to Search and Replace	1	301368

Description

Searching is useful. However, you can make searching even more powerful when it also changes (or replaces) the text you match. You can search and replace text in a string using .replace() on a string. The inputs for .replace() 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.

let wrongText = "The sky is silver.";
let silverRegex = /silver/;
wrongText.replace(silverRegex, "blue");
// Returns "The sky is blue."

You can also access capture groups in the replacement string with dollar signs ($).

"Code Camp".replace(/(\w+)\s(\w+)/, '$2 $1');
// Returns "Camp Code"

Instructions

Write a regex fixRegex using three capture groups that will search for each word in the string "one two three". Then update the replaceText variable to replace "one two three" with the string "three two one" and assign the result to the result variable. Make sure you are utilizing capture groups in the replacement string using the dollar sign ($) syntax.

Tests

tests:
  - text: You should use <code>.replace()</code> to search and replace.
    testString: assert(code.match(/\.replace\(.*\)/));
  - text: Your regex should change <code>"one two three"</code> to <code>"three two one"</code>
    testString: assert(result === "three two one");
  - text: You should not change the last line.
    testString: assert(code.match(/result\s*=\s*str\.replace\(.*?\)/));
  - text: <code>fixRegex</code> should use at least three capture groups.
    testString: assert((new RegExp(fixRegex.source + '|')).exec('').length - 1 >= 3);
  - text: <code>replaceText</code> should use parenthesized submatch string(s) (i.e. the nth parenthesized submatch string, $n, corresponds to the nth capture group).
    testString: '{
      const re = /(\$\d{1,2})+(?:[\D]|\b)/g;
      assert(replaceText.match(re).length >= 3);
    }'

Challenge Seed

let str = "one two three";
let fixRegex = /change/; // Change this line
let replaceText = ""; // Change this line
let result = str.replace(fixRegex, replaceText);

Solution

let str = "one two three";
let fixRegex = /(\w+) (\w+) (\w+)/g; // Change this line
let replaceText = "$3 $2 $1"; // Change this line
let result = str.replace(fixRegex, replaceText);