Regular Expressions - Reuse Patterns Using Capture Groups

JavaScript
1

Understanding Capture groups :
Hi, can anyone explain why this code works… I don’t really understand it.
Thanks, have a great day!

Your code so far

let repeatNum = "42 42 42";
let reRegex = /^(\d+) \1 \1$/; 
let result = reRegex.test(repeatNum);

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Challenge: Regular Expressions - Reuse Patterns Using Capture Groups

Link to the challenge:

2

I spoilered the code because it is a solution.
Can you explain the bits which you do and do not understand about that regex?