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  <title>Array with() — vs mutate</title>
</head>
<body>
  <h1>with() vs arr[i] =</h1>
  <pre id="out"></pre>
  <script>
    (function () {
      var immutable = [10, 20, 30];
      var mutable = [10, 20, 30];
      var next = immutable.with(1, 99);
      mutable[1] = 99;
      document.getElementById("out").textContent =
        "immutable original: " + JSON.stringify(immutable) + "\n" +
        "with result: " + JSON.stringify(next) + "\n" +
        "mutable after [1]=: " + JSON.stringify(mutable);
    })();
  </script>
</body>
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JavaScript Array with() — vs mutation (Try It)