reproduce the issue

Author: nathanfallet

core/src/jvmTest/kotlin/dev/kdriver/core/dom/ReactControlledInputTest.kt

@@ -0,0 +1,116 @@
+package dev.kdriver.core.dom
+
+import dev.kdriver.core.browser.createBrowser
+import dev.kdriver.core.sampleFile
+import dev.kdriver.core.tab.ReadyState
+import dev.kdriver.core.tab.evaluate
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.runBlocking
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+/**
+ * Tests that reproduce the React controlled input silent failure bug.
+ *
+ * React installs an instance-level value property setter on controlled inputs
+ * (its _valueTracker mechanism). Direct `el.value = x` assignments go through
+ * this setter, updating the tracker's "last known value". When an 'input' event
+ * then fires, React checks `el.value === tracker.getValue()` — they match —
+ * so React concludes nothing changed and does NOT call onChange.
+ *
+ * kdriver's clearInput() and clearInputByDeleting() both use direct `.value`
+ * assignments, making them silently ineffective against React controlled inputs.
+ * The real-world consequence is a "mixed value" when filling a pre-filled input
+ * (e.g. old value "10", new value "25" → result "1025").
+ */
+class ReactControlledInputTest {
+
+    /**
+     * clearInput() uses `element.value = ""` which goes through React's tracker setter,
+     * updating both the DOM and trackerValue to "". No 'input' event is dispatched,
+     * so React's onChange check never runs. React state stays at "10".
+     */
+    @Test
+    fun testClearInputDoesNotNotifyReact() = runBlocking {
+        val browser = createBrowser(this, headless = true, sandbox = false)
+        val tab = browser.get(sampleFile("react-controlled-input-test.html"))
+        tab.waitForReadyState(ReadyState.COMPLETE)
+
+        val input = tab.select("#controlled-input")
+
+        assertEquals("10", tab.evaluate<String>("document.getElementById('state-value').textContent"))
+        assertEquals("0", tab.evaluate<String>("document.getElementById('change-count').textContent"))
+
+        input.clearInput()
+        delay(100)
+
+        // Expected: React state is "" (the clear was communicated to React)
+        // Actual:   React state is still "10" (React was never notified)
+        assertEquals("", tab.evaluate<String>("document.getElementById('state-value').textContent"))
+
+        browser.stop()
+    }
+
+    /**
+     * clearInputByDeleting() uses `el.value = el.value.slice(1)` on each iteration.
+     * Each direct .value assignment goes through React's tracker setter, updating both
+     * the DOM and trackerValue simultaneously. When the 'input' event fires afterwards,
+     * React checks `el.value === trackerValue` — they match — so onChange is never called.
+     * React state stays at "10".
+     */
+    @Test
+    fun testClearInputByDeletingDoesNotNotifyReact() = runBlocking {
+        val browser = createBrowser(this, headless = true, sandbox = false)
+        val tab = browser.get(sampleFile("react-controlled-input-test.html"))
+        tab.waitForReadyState(ReadyState.COMPLETE)
+
+        val input = tab.select("#controlled-input")
+
+        assertEquals("10", tab.evaluate<String>("document.getElementById('state-value').textContent"))
+        assertEquals("0", tab.evaluate<String>("document.getElementById('change-count').textContent"))
+
+        input.clearInputByDeleting()
+        delay(100)
+
+        // Expected: React state is "" (every deletion was communicated to React)
+        // Actual:   React state is still "10" (silent failure — tracker matched on each event)
+        assertEquals("", tab.evaluate<String>("document.getElementById('state-value').textContent"))
+
+        browser.stop()
+    }
+
+    /**
+     * The real-world consequence: after clearInputByDeleting silently fails to notify React,
+     * React's async scheduler re-renders and restores the DOM to its controlled value ("10").
+     * insertText("25") then inserts into "10" instead of an empty field, producing a mixed
+     * value like "1025" instead of the intended "25".
+     */
+    @Test
+    fun testFillReactControlledInputProducesMixedValue() = runBlocking {
+        val browser = createBrowser(this, headless = true, sandbox = false)
+        val tab = browser.get(sampleFile("react-controlled-input-test.html"))
+        tab.waitForReadyState(ReadyState.COMPLETE)
+
+        val input = tab.select("#controlled-input")
+
+        // Step 1: Try to clear — silently fails at React level, DOM appears empty
+        input.clearInputByDeleting()
+
+        // Step 2: Simulate React's async re-render committing the old controlled state.
+        // In a real app this happens automatically (React's scheduler) between operations.
+        // React uses the native prototype setter to revert the DOM to "10".
+        tab.evaluate<String>("window.simulateReactRerender();'done'")
+        delay(50)
+
+        // Step 3: Insert the new value — but DOM now holds "10", not ""
+        input.insertText("25")
+        delay(100)
+
+        // Expected: "25"   (clear worked, so inserting into empty field gives "25")
+        // Actual:   "1025" (inserted at end of "10" that React restored)
+        assertEquals("25", input.getInputValue())
+
+        browser.stop()
+    }
+
+}

core/src/jvmTest/resources/react-controlled-input-test.html

@@ -0,0 +1,86 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <title>React Controlled Input Test</title>
+    <script>
+        window.onload = function () {
+            const input = document.getElementById('controlled-input');
+            const stateDisplay = document.getElementById('state-value');
+            const changeCount = document.getElementById('change-count');
+
+            // Simulated React state
+            let reactState = '10';
+            let changeCallCount = 0;
+
+            // Save the native prototype getter/setter before installing the tracker.
+            const nativeDescriptor = Object.getOwnPropertyDescriptor(HTMLInputElement.prototype, 'value');
+            const nativeSetter = nativeDescriptor.set;
+            const nativeGetter = nativeDescriptor.get;
+
+            // React's _valueTracker: remembers the last value that went through the
+            // instance-level setter so React can tell whether a change is genuinely new.
+            let trackerValue;
+
+            // Install React's instance-level value property on this specific DOM node.
+            // This is exactly what React does internally when it first renders a controlled input.
+            // Direct assignments (el.value = x) go through this setter, updating the tracker.
+            Object.defineProperty(input, 'value', {
+                configurable: true,
+                get: function () {
+                    return nativeGetter.call(this);
+                },
+                set: function (val) {
+                    trackerValue = '' + val;       // tracker records the assignment
+                    nativeSetter.call(this, val);  // actual DOM value update
+                }
+            });
+
+            // Set the initial controlled value through the tracker (as React does on commit).
+            input.value = reactState;  // → trackerValue = "10", DOM = "10"
+
+            // React's change detection: fires onChange only when the new DOM value
+            // differs from what the tracker last recorded.
+            input.addEventListener('input', function () {
+                const currentDOMValue = nativeGetter.call(input);
+
+                if (currentDOMValue === trackerValue) {
+                    // DOM value matches tracker → React concludes "I already knew about this"
+                    // → onChange is NOT fired → state remains unchanged
+                    return;
+                }
+
+                // Values differ → genuine change detected → fire onChange
+                changeCallCount++;
+                reactState = currentDOMValue;
+                trackerValue = currentDOMValue;
+                stateDisplay.textContent = reactState;
+                changeCount.textContent = String(changeCallCount);
+            });
+
+            stateDisplay.textContent = reactState;
+            changeCount.textContent = '0';
+
+            // Simulates React committing a re-render with the current controlled state.
+            // In a real React app, the async scheduler does this between user operations.
+            // Uses the native prototype setter directly (bypassing the tracker instance property),
+            // which is exactly what React's commit phase does.
+            window.simulateReactRerender = function () {
+                nativeSetter.call(input, reactState);
+                trackerValue = reactState;
+            };
+        };
+    </script>
+</head>
+<body>
+<h1>React Controlled Input Simulation</h1>
+<p>Simulates a React-controlled input to reproduce the _valueTracker silent failure bug.</p>
+<div>
+    <label for="controlled-input">Price:</label>
+    <input id="controlled-input" type="text"/>
+</div>
+<div>
+    <p>React state: <span id="state-value">10</span></p>
+    <p>onChange calls: <span id="change-count">0</span></p>
+</div>
+</body>
+</html>