Forms · Complete runnable example

Bounded autogrow textarea

Give a short working note room to grow without letting it fill the page.

Try the example Read and copy the source

Live example

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When to use it

Use a growing textarea for short notes where readers benefit from seeing more of their text. The example caps its height at 240px and leaves longer content scrollable.

Try the important details

  1. Type several lines or paste a paragraph and watch the field grow to its height limit.
  2. Delete most of the text to check that the field shrinks again.
  3. Enter emoji and compare the count, then clear the note and confirm focus returns to the textarea.

How it works

  • Each input event resets height to auto before measuring scrollHeight, which permits both growth and shrinkage.
  • The measured height is bounded between 112px and 240px. Window resizing recalculates wrapped content.
  • The 400-unit native maxlength and JavaScript string length both use UTF-16 code units, so some emoji consume multiple units. No storage is used.

The complete source

The preview, copied text, and downloaded file use this same document.

HTML 

<!doctype html>
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SOFTWARE.
-->
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <meta
      http-equiv="Content-Security-Policy"
      content="default-src 'none'; style-src 'unsafe-inline'; script-src 'unsafe-inline'; img-src data: blob:; connect-src 'none'; form-action 'none'; object-src 'none'; base-uri 'none'"
    />
    <title>Room for a thought. | MRHTML example</title>
    <style>
      :root {
        color-scheme: light;
        --ink: #202b36;
        --muted: #596675;
        --line: #d5dde4;
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        --danger: #a32b30;
        font-family: Arial, Helvetica, sans-serif;
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      * {
        box-sizing: border-box;
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      [hidden] {
        display: none !important;
      }
      body {
        margin: 0;
        min-width: 0;
        padding: 42px 22px;
        background: #f2f4f7;
        color: var(--ink);
        line-height: 1.55;
      }
      main {
        max-width: 690px;
        margin: auto;
      }
      .brand {
        display: flex;
        align-items: center;
        gap: 10px;
        margin: 0 0 25px;
        color: var(--muted);
        font-size: 12px;
        letter-spacing: 0.04em;
      }
      .brand b {
        color: var(--ink);
        letter-spacing: -0.05em;
        font-size: 17px;
      }
      .brand b span {
        color: var(--blue);
      }
      .brand i {
        flex: 1;
        height: 1px;
        background: var(--line);
      }
      .card {
        background: var(--paper);
        border: 1px solid var(--line);
        border-radius: 18px;
        padding: 32px;
        box-shadow: 0 12px 36px #263a5110;
      }
      .eyebrow {
        margin: 0 0 12px;
        font-size: 11px;
        font-weight: 700;
        text-transform: uppercase;
        letter-spacing: 0.12em;
        color: var(--blue);
      }
      h1 {
        font-size: clamp(29px, 5vw, 38px);
        line-height: 1.13;
        letter-spacing: -0.04em;
        margin: 0 0 14px;
      }
      h2 {
        font-size: 20px;
        line-height: 1.3;
        margin: 0 0 14px;
      }
      p {
        margin: 0 0 18px;
      }
      .intro {
        color: var(--muted);
        max-width: 55ch;
      }
      .hint,
      .small {
        font-size: 13px;
        color: var(--muted);
      }
      .hint {
        margin: 9px 0 0;
      }
      .footer {
        font-size: 12px;
        color: var(--muted);
        margin: 20px 2px 0;
      }
      label,
      legend {
        font-weight: 700;
        font-size: 14px;
      }
      label.field {
        display: block;
        margin: 18px 0 7px;
      }
      fieldset {
        min-width: 0;
        margin: 22px 0;
        padding: 20px;
        border: 1px solid var(--line);
        border-radius: 10px;
      }
      legend {
        padding: 0 7px;
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      input,
      select,
      textarea,
      button {
        font: inherit;
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      input:not([type='checkbox']):not([type='radio']),
      select,
      textarea {
        width: 100%;
        min-width: 0;
        color: var(--ink);
        background: #fff;
        border: 1px solid #8896a5;
        border-radius: 7px;
        padding: 11px 12px;
        font-size: 16px;
      }
      input[type='checkbox'],
      input[type='radio'] {
        accent-color: var(--blue);
        width: 18px;
        height: 18px;
        flex: none;
      }
      textarea {
        display: block;
        resize: vertical;
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      button {
        border: 1px solid var(--blue);
        border-radius: 7px;
        min-height: 44px;
        padding: 10px 17px;
        background: var(--blue);
        color: #fff;
        font-size: 14px;
        font-weight: 700;
        cursor: pointer;
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      button.secondary {
        background: #fff;
        color: var(--blue);
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      button:disabled {
        cursor: default;
        opacity: 0.55;
      }
      input:disabled,
      select:disabled {
        background: #f0f2f5;
        color: #596675;
      }
      :focus-visible {
        outline: 3px solid #d46a20;
        outline-offset: 3px;
      }
      .actions {
        display: flex;
        flex-wrap: wrap;
        gap: 10px;
        margin-top: 22px;
      }
      .status {
        margin: 18px 0 0;
        font-size: 14px;
        min-height: 1.6em;
      }
      .error {
        color: var(--danger);
      }
      .panel {
        background: var(--pale);
        padding: 20px;
        border-radius: 10px;
        margin-top: 24px;
      }
      .panel p:last-child {
        margin-bottom: 0;
      }
      .row {
        display: flex;
        gap: 12px;
        align-items: center;
      }
      .sr {
        position: absolute;
        width: 1px;
        height: 1px;
        margin: -1px;
        overflow: hidden;
        clip: rect(0, 0, 0, 0);
        white-space: nowrap;
      }
      noscript p {
        border-left: 3px solid #9b6300;
        background: #fff4d6;
        padding: 12px;
        font-size: 14px;
        margin-top: 20px;
      }
      code {
        overflow-wrap: anywhere;
      }
      @media (max-width: 450px) {
        body {
          padding: 25px 14px;
        }
        .card {
          padding: 23px 19px;
          border-radius: 13px;
        }
        fieldset {
          padding: 16px 13px;
        }
        .brand {
          margin-bottom: 18px;
        }
      }
      @media (prefers-reduced-motion: reduce) {
        *,
        *::before,
        *::after {
          animation: none !important;
          transition: none !important;
          scroll-behavior: auto !important;
        }
      }

      #growing-note {
        min-height: 112px;
        max-height: 240px;
        line-height: 1.7;
        background: repeating-linear-gradient(
          #fff,
          #fff 26px,
          #edf1f6 27px,
          #fff 28px
        );
        background-origin: content-box;
      }
      .note-meta {
        display: flex;
        justify-content: space-between;
        gap: 12px;
      }
      #count {
        flex: none;
        font-variant-numeric: tabular-nums;
      }
    </style>
  </head>
  <body>
    <main>
      <p class="brand">
        <b>MR<span>HTML</span></b
        ><span>THE INTERACTION NOTEBOOK</span><i aria-hidden="true"></i>
      </p>
      <section class="card" aria-labelledby="title">
        <p class="eyebrow">04 / Autogrow textarea</p>
        <h1 id="title">Room for a thought.</h1>
        <p class="intro">
          A short note field that grows as you write and shrinks when you remove
          text. Try a few lines or paste a paragraph.
        </p>
        <label class="field" for="growing-note">Working note</label
        ><textarea
          id="growing-note"
          rows="3"
          maxlength="400"
          aria-describedby="note-help count"
          placeholder="Start with one small idea..."
        ></textarea>
        <div class="note-meta">
          <p id="note-help" class="hint">
            Temporary text. Up to 400 UTF-16 code units.
          </p>
          <p id="count" class="hint" hidden>0 / 400</p>
        </div>
        <div class="actions">
          <button id="clear-note" type="button" class="secondary" disabled>
            Clear note
          </button>
        </div>
        <p id="note-status" class="status" role="status">
          Automatic resizing starts when the script is ready.
        </p>
        <div class="panel">
          <p class="small">
            The field stops growing at 240px and scrolls internally. Some emoji
            use two or more code units; this counter matches the browser's
            maxlength rule.
          </p>
        </div>
        <noscript
          ><p>
            The native textarea remains editable and manually resizable with its
            400-code-unit limit. Automatic height and the counter require
            JavaScript.
          </p></noscript
        >
      </section>
      <p class="footer">A local MRHTML example. Nothing is sent or saved.</p>
    </main>
    <script>
      (function () {
        'use strict';

        var note = document.getElementById('growing-note'),
          count = document.getElementById('count'),
          clear = document.getElementById('clear-note'),
          status = document.getElementById('note-status');
        function resize() {
          note.style.height = 'auto';
          var height = Math.max(112, Math.min(240, note.scrollHeight + 2));
          note.style.height = height + 'px';
          note.style.overflowY =
            note.scrollHeight + 2 > 240 ? 'auto' : 'hidden';
          count.textContent = note.value.length + ' / 400';
        }
        note.addEventListener('input', function () {
          resize();
          status.textContent = 'Note stays in this page only.';
        });
        clear.addEventListener('click', function () {
          note.value = '';
          resize();
          status.textContent = 'Note cleared. Nothing was saved.';
          note.focus();
        });
        window.addEventListener('resize', resize);
        note.style.resize = 'none';
        count.hidden = false;
        clear.disabled = false;
        resize();
        status.textContent = 'Ready. Nothing is sent or saved.';
      })();
    </script>
  </body>
</html>