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79 lines
3.4 KiB
HTML
79 lines
3.4 KiB
HTML
<!doctype html>
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<meta charset="utf-8">
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<title>20 React _valueTracker</title>
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<link rel="stylesheet" href="../_style.css">
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<script src="../_lib.js"></script>
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<body>
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<main>
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<p>Goal: set the input to <code>react-ok</code> in a way that React would accept.
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The page mimics React's <code>_valueTracker</code>: it stamps the input with a
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hidden tracker holding the last-seen value. An <code>input</code> event is only
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considered "framework-real" if the tracker's recorded value differs from the
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current <code>input.value</code> at the moment the event fires
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(i.e. somebody used the native <code>HTMLInputElement.value</code> setter and
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dispatched <code>input</code> — what React internals require).</p>
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<p>Setting <code>el.value = ...</code> directly and dispatching a synthetic <code>input</code>
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fails because the native setter wasn't used. Calling <code>setRangeText</code> without
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dispatching <code>input</code> also fails.</p>
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<input id="t" placeholder="type or fill 'react-ok'" style="font-size:18px;padding:8px 12px;width:240px">
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</main>
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<script>
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Challenge.init({ id: "react-value-tracker", instructions: "make input value 'react-ok' as React expects" });
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const t = document.getElementById("t");
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// Install a fake React-style _valueTracker.
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(function attachTracker(node) {
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const nativeProto = Object.getPrototypeOf(node);
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const desc = Object.getOwnPropertyDescriptor(nativeProto, "value");
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const nativeGet = desc.get, nativeSet = desc.set;
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let tracked = nativeGet.call(node); // last value the "framework" has seen
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node._valueTracker = {
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getValue() { return tracked; },
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setValue(v) { tracked = v; },
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};
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// Wrap the value property on the *instance* to intercept assignments.
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Object.defineProperty(node, "value", {
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configurable: true,
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get() { return nativeGet.call(this); },
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set(v) {
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// If somebody assigns via instance property (the bad path), sync the tracker
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// so the input event below will look "stale" and we can detect it.
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tracked = String(v);
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nativeSet.call(this, v);
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},
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});
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})(t);
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let passed = false;
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t.addEventListener("input", (e) => {
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if (passed) return;
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const proto = Object.getPrototypeOf(t);
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const nativeGet = Object.getOwnPropertyDescriptor(proto, "value").get;
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const real = nativeGet.call(t);
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const tracked = t._valueTracker.getValue();
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Challenge.log("input", { real, tracked, isTrusted: e.isTrusted });
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if (real !== "react-ok") return;
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if (!e.isTrusted && tracked === real) {
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return Challenge.fail("synthetic input event but _valueTracker already up-to-date (instance value= setter used, not native)");
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}
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// The "good" path: native setter ran (tracker still stale), then input dispatched.
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// After the framework consumes the event it would syncs the tracker.
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t._valueTracker.setValue(real);
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passed = true;
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Challenge.pass(`value 'react-ok' delivered with stale tracker (native setter path); isTrusted=${e.isTrusted}`);
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});
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// Trap: value mutates without input ever firing.
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setInterval(() => {
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if (passed) return;
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const proto = Object.getPrototypeOf(t);
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const nativeGet = Object.getOwnPropertyDescriptor(proto, "value").get;
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if (nativeGet.call(t) === "react-ok" && !passed) {
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// Only fail if we've been sitting on the value with no event for a while.
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setTimeout(() => { if (!passed && nativeGet.call(t) === "react-ok") Challenge.fail("value='react-ok' but no input event consumed it"); }, 600);
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}
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}, 300);
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</script>
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</body>
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