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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>chain — tap</title>
</head>
<body>
  <h1>With tap</h1>
  <pre id="out"></pre>
  <script src="https://cdn.jsdelivr.net/npm/lodash@4.17.21/lodash.min.js"></script>
  <script>
    var seen = null;
    var result = _.chain([1, 2, 3])
      .map(function (n) { return n * 2; })
      .tap(function (arr) { seen = arr.slice(); })
      .filter(function (n) { return n > 2; })
      .value();
    document.getElementById("out").textContent =
      JSON.stringify(result) + "\n" +
      JSON.stringify(seen);
  </script>
</body>
</html>

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Lodash _.chain — tap (Try It)