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HTML

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Insecure Resource

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CSS

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CSS Base

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JavaScript

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JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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Packages

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Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

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HTML 

              
                <h1>Happy Fibonacci day!</h1>
<p>
  Maybe I'm a day late. Sorry. Here's a way to calculate the Fibonacci Sequence using vanilla JavaScript with recursion. It gets a lot faster <i>without recursion</i>, though. <br>
  This version is optimized so it's almost as fast as the iterative solution, but this solution is a little prettier and could be written as a one-liner.<br>
  In mathematics, the Fibonacci sequence is characterized by every number after the first two being the sum of the two preceding numbers:<br/>
  <code>
    1, 1, 2, 3, 5, 8, 13, 21, 34, ...
  </code><br/>
  Often, especially in modern usage, the sequence is preceded by a zero:<br/>
  <code>
    0, 1, 1, 2, 3, 5, 8, 13, 21, 34, ...
  </code><br/>
  November 23 (11/23) is Fibonacci day because when the date is written in the MM/DD format, the digits are the start of the sequence: 1,1,2,3
</p>
<p id='result'></p>
!

CSS 

              
                body {
  padding: 1em;
}
#result {
  font-family: monospace;
  padding: .3em;
  background: black;
  color: green;
}
!

JS 

              
                const r = Array();
function optimizedFib(n, a = 1, b = 0) {
  r.push(b);
  if (n === 0) {
    return b;
  }
  return optimizedFib(n - 1, a + b, a);
}

optimizedFib(1000);
var out = document.getElementById('result');
r.forEach(el => {
  result.append(el + ", ");
})
!
999px

Console