title: What does $1 do in jest config?
body: <p>The <a href="https://facebook.github.io/jest/docs/webpack.html" rel="noreferrer">tutorial</a> for using jest with webpack mentions this syntax: $1, and I haven't been able to figure out what it does. I'm working on two projects with the same aliases, but one works with jest config:</p>
  
  <pre><code>"moduleNameMapper": {
    "^myModule(.*)$": "&lt;rootDir&gt;/src/components/react",
  }
  </code></pre>
  
  <p>while one works with</p>
  
  <pre><code>"moduleNameMapper": {
    "^myModule(.*)$": "&lt;rootDir&gt;/src/components/react$1",
  }
  </code></pre>
  
  <p>What does the $1 syntax do?</p>