bug(input_text_area): Auto resized text areas resize on visibility change

CHANGELOG.md

@@ -19,6 +19,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * Require shinyswatch >= 0.7.0 and updated examples accordingly. (#1558)
 
+* `input_text_area(autoresize=True)` now resizes properly even when it's not visible when initially rendered (e.g. in a closed accordion or a hidden tab). (#1560)
+
 ### Bug fixes
 
 ### Deprecations

js/text-area/textarea-autoresize.ts

@@ -18,10 +18,46 @@ function onDelegatedEvent(
   });
 }
 
+// Use a single intersectionObserver as they are slow to create / use.
+let textAreaIntersectionObserver: null | IntersectionObserver = null;
+
+function callUpdateHeightWhenTargetIsVisible(target: HTMLTextAreaElement) {
+  if (textAreaIntersectionObserver === null) {
+    // Create a single observer to watch for the textarea becoming visible
+    textAreaIntersectionObserver = new IntersectionObserver(
+      (entries, observer) => {
+        entries.forEach((entry) => {
+          // Quit if the entry is not visible
+          if (!entry.isIntersecting) {
+            return;
+          }
+          // If the entry is visible (even if it's just a single pixel)
+          // Stop observing the target
+          textAreaIntersectionObserver!.unobserve(entry.target);
+
+          // Update the height of the textarea
+          update_height(entry.target as HTMLTextAreaElement);
+        });
+      }
+    );
+  }
+
+  textAreaIntersectionObserver.observe(target);
+}
+
 function update_height(target: HTMLTextAreaElement) {
-  // Automatically resize the textarea to fit its content.
-  target.style.height = "auto";
-  target.style.height = target.scrollHeight + "px";
+  if (target.scrollHeight > 0) {
+    // Automatically resize the textarea to fit its content.
+    target.style.height = "auto";
+    target.style.height = target.scrollHeight + "px";
+  } else {
+    // The textarea is not visible on the page, therefore it has a 0 scroll height.
+
+    // If we should autoresize the text area height, then we can wait for the textarea to
+    // become visible and call `update_height` again. Hopefully the scroll height is no
+    // longer 0
+    callUpdateHeightWhenTargetIsVisible(target);
+  }
 }
 
 // Update on change

shiny/www/py-shiny/text-area/textarea-autoresize.js

@@ -7,9 +7,30 @@ function onDelegatedEvent(eventName, selector, callback) {
     }
   });
 }
+var textAreaIntersectionObserver = null;
+function callUpdateHeightWhenTargetIsVisible(target) {
+  if (textAreaIntersectionObserver === null) {
+    textAreaIntersectionObserver = new IntersectionObserver(
+      (entries, observer) => {
+        entries.forEach((entry) => {
+          if (!entry.isIntersecting) {
+            return;
+          }
+          textAreaIntersectionObserver.unobserve(entry.target);
+          update_height(entry.target);
+        });
+      }
+    );
+  }
+  textAreaIntersectionObserver.observe(target);
+}
 function update_height(target) {
-  target.style.height = "auto";
-  target.style.height = target.scrollHeight + "px";
+  if (target.scrollHeight > 0) {
+    target.style.height = "auto";
+    target.style.height = target.scrollHeight + "px";
+  } else {
+    callUpdateHeightWhenTargetIsVisible(target);
+  }
 }
 onDelegatedEvent(
   "input",

tests/playwright/shiny/inputs/input_text_area/autoresize/app.py

@@ -0,0 +1,26 @@
+from shiny.express import render, ui
+
+with ui.navset_card_tab(id="tab"):
+
+    with ui.nav_panel("Tab 1"):
+        "Tab 1 content"
+    with ui.nav_panel("Text Area"):
+        ui.input_text_area(
+            id="test_text_area",
+            label="A text area input",
+            autoresize=True,
+            value="a\nb\nc\nd\ne",
+        )
+
+        ui.input_text_area(
+            id="test_text_area2",
+            label="A second text area input",
+            autoresize=True,
+            value="a\nb\nc\nd\ne",
+            rows=4,
+        )
+
+
+@render.code
+def text():
+    return "Loaded"

tests/playwright/shiny/inputs/input_text_area/autoresize/test_accordion_autoresize.py

@@ -0,0 +1,47 @@
+from playwright.sync_api import Page
+
+from shiny.playwright import controller
+from shiny.playwright.expect import expect_to_have_style
+from shiny.run import ShinyAppProc
+
+
+def test_accordion(page: Page, local_app: ShinyAppProc, is_webkit: bool) -> None:
+    page.goto(local_app.url)
+
+    text = controller.OutputCode(page, "text")
+    tab = controller.NavsetTab(page, "tab")
+
+    test_text_area = controller.InputTextArea(page, "test_text_area")
+    test_text_area_w_rows = controller.InputTextArea(page, "test_text_area2")
+
+    text.expect_value("Loaded")
+
+    # Make sure the `rows` is respected
+    test_text_area_w_rows.expect_rows("4")
+    # Make sure the placeholder row value of `1` is set
+    test_text_area.expect_rows("1")
+
+    tab.set("Text Area")
+
+    test_text_area.expect_autoresize(True)
+    test_text_area.expect_value("a\nb\nc\nd\ne")
+
+    if is_webkit:
+        # Skip the rest of the test for webkit.
+        # Heights are not consistent with chrome and firefox
+        return
+    expect_to_have_style(test_text_area.loc, "height", "125px")
+    expect_to_have_style(test_text_area_w_rows.loc, "height", "125px")
+
+    # Make sure the `rows` is consistent
+    test_text_area.expect_rows("1")
+    test_text_area_w_rows.expect_rows("4")
+
+    # Reset the text area to a single row and make sure the area shrink to appropriate size
+    test_text_area.set("single row")
+    test_text_area_w_rows.set("single row")
+
+    # 1 row
+    expect_to_have_style(test_text_area.loc, "height", "35px")
+    # 4 rows
+    expect_to_have_style(test_text_area_w_rows.loc, "height", "102px")