freeCodeCamp Challenge Guide: Reuse Patterns Using Capture Groups

Guide
1

Reuse Patterns Using Capture Group

Hints

Hint 1

Given code below:

let testString = "test test test";
let reRegex = /(test)\s\1/;
let result = reRegex.test(testString);

result will match only test test because \1 in this example stands for the same text as most recently matched by the 1st capturing group (test).

If we were to literally translate the regex, it would look something like this:

let re = /(test)\s\1/;
let literalRe = /test\stest/;

Both re and literalRe would match the same thing.

Hint 2

Given the code below:

let testString = "test test test";
let reRegex = /(test)(\s)\1\2\1/;
let result = reRegex.test(testString);

result will match whole test test test because:
\1 repeats (test)
\2 repeats (\s)

Hint 3

The code below:

let testString = "test test test test test test";
let reRegex = /(test)(\s)\1\2\1/g;
let result = reRegex.test(testString);

because we used \g, our Regex doesn’t return after first full match (test test test) and matched all repetitions. Think about how you can assert the start and end of the string.

Solutions

Solution 1 (Click to Show/Hide) 
let repeatNum = "42 42 42";
let reRegex = /^(\d+) \1 \1$/;
let result = reRegex.test(repeatNum);
Solution 2 (Click to Show/Hide) 
let repeatNum = "42 42 42";
let reRegex = /^(\d+) \1 \1(?!.)/; // Change this line
let result = reRegex.test(repeatNum);
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