WebReflection · March 3, 2025 21:05 · Mar 3, 2025 · Mar 3, 2025
diff --git a/ten-tdec.md b/ten-tdec.md
@@ -31,7 +31,7 @@ rbuff.set(ref, 0); // ✅
 
 ### TextDecoder
 
-Only an `ArrayBuffer`, *resiable* or not, can be used. `SharedArray` needs to be sliced as static `ArrayBuffer`.
+Only an `ArrayBuffer`, *resizable* or not, can be used. `SharedArray` needs to be sliced as static `ArrayBuffer`.
 
 ```js
 const decoder = new TextDecoder;

diff --git a/ten-tdec.md b/ten-tdec.md
@@ -0,0 +1,76 @@
+# TextEncoder & TextDecoder shenanigans
+
+This gist is to remind developers that resizable or growable *buffers* don't play nice with `TextEncoder` or `TextDecoder` instances.
+
+### Setup
+
+```js
+// setup
+const ref = new TextEncoder().encode("hello");
+
+// SharedArrayBuffer (static) View
+const sab = new Uint8Array(new SharedArrayBuffer(5));
+// optional pre-populate
+sab.set(ref, 0); // ✅
+
+// SharedArrayBuffer (growable) View
+const gsab = new Uint8Array(new SharedArrayBuffer(5, { maxByteLength: 16 }));
+// optional pre-populate
+gsab.set(ref, 0); // ✅
+
+// ArrayBuffer (static) View
+const buff = new Uint8Array(new ArrayBuffer(5));
+// optional pre-populate
+buff.set(ref, 0); // ✅
+
+// ArrayBuffer (resizable) View
+const rbuff = new Uint8Array(new ArrayBuffer(5, { maxByteLength: 16 }));
+// optional pre-populate
+rbuff.set(ref, 0); // ✅
+```
+
+### TextDecoder
+
+Only an `ArrayBuffer`, *resiable* or not, can be used. `SharedArray` needs to be sliced as static `ArrayBuffer`.
+
+```js
+const decoder = new TextDecoder;
+
+decoder.decode(buff); // ✅
+decoder.decode(rbuff); // ✅
+decoder.decode(sab.slice(0)); // ✅ - not shared
+decoder.decode(gsab.slice(0)); // ✅ - not shared
+
+decoder.decode(sab); // ❌
+// Failed to execute 'decode' on 'TextDecoder':
+// The provided ArrayBufferView value must not be shared.
+
+decoder.decode(gsab); // ❌
+decoder.decode(gsab.subarray(0)); // ❌
+// Failed to execute 'decode' on 'TextDecoder':
+// The provided ArrayBufferView value must not be shared.
+```
+
+### TextEncoder encodeInto
+
+Only **static** `ArrayBuffer` can be used, making it impossible to use for linear, resizable, serializations purposes.
+
+```js
+const encoder = new TextEncoder;
+
+encoder.encodeInto("hello", buff); // ✅
+
+encoder.encodeInto("hello", gsab); // ❌
+encoder.encodeInto("hello", gsab.subarray(0)); // ❌
+// Failed to execute 'encodeInto' on 'TextEncoder':
+// The provided Uint8Array value must not be shared.
+
+encoder.encodeInto("hello", rbuff); // ❌
+encoder.encodeInto("hello", rbuff.subarray(0)); // ❌
+// Failed to execute 'encodeInto' on 'TextEncoder':
+// The provided Uint8Array value must not be resizable.
+```
+
+- - -
+
+Related topic in TC39 around the fact we can't even know AOT the size of a string before deciding to use awkward magic behind the scene to make `encodeInto` happen: https://es.discourse.group/t/string-bytelength-count/2315