freeCodeCamp/use-capture-groups-to-search-and-replace.english.md at bfe76794c069c492202512d29b09e3b134a5d943

Arthur 616d96f612 refactor: update trivial regex capture group find and replace challenge (#37768 )

* refactor: replace trivial regex capture group challenge

Previous challenge could be completed without any capture groups. New
challenge requires 3 capture groups and 3 uses of the submatches in the
replacement.

resolves #17645

* test: validate at least 3 capture groups were used

Use solution from SO
(https://stackoverflow.com/questions/16046620/regex-to-count-the-number-of-capturing-groups-in-a-regex)
as suggested by @RandellDawson to count the number of capturing
groups, regardless of whether or not the regex in question solves the
broader problem.

Co-Authored-By: Randell Dawson <5313213+RandellDawson@users.noreply.github.com>

* refactor: more meaningful variable name

Co-Authored-By: Randell Dawson <5313213+RandellDawson@users.noreply.github.com>

* test: add parenthesized substring test

* test: ensure 3 uses of substring replacement

* refactor: reword instructions

* fix: minor grammar fix

Co-Authored-By: Manish Giri <manish.giri.me@gmail.com>

* refactor: elaborate wording in test

2019-12-14 16:41:47 -05:00

2.7 KiB

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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);

2.7 KiB Raw Blame History