proposal-arraybuffer-base64 Uint8Array.prototype.set* methods backed by an immutable ArrayBuffer

Author: gibson042

test/built-ins/Uint8Array/prototype/setFromBase64/immutable-buffer.js

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+// Copyright (C) 2025 Richard Gibson. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-uint8array.prototype.setfrombase64
+description: Throws a TypeError exception when the backing buffer is immutable
+info: |
+  Uint8Array.prototype.setFromBase64 ( string [ , options ] )
+  1. Let into be the this value.
+  2. Perform ? ValidateUint8Array(into).
+  3. If string is not a String, throw a TypeError exception.
+  4. Let opts be ? GetOptionsObject(options).
+  5. Let alphabet be ? Get(opts, "alphabet").
+  6. If alphabet is undefined, set alphabet to "base64".
+  7. If alphabet is neither "base64" nor "base64url", throw a TypeError exception.
+  8. Let lastChunkHandling be ? Get(opts, "lastChunkHandling").
+features: [TypedArray, uint8array-base64, immutable-arraybuffer]
+includes: [testTypedArray.js, compareArray.js]
+---*/
+
+testWithAllTypedArrayConstructors((TA, makeCtorArg) => {
+  var calls = [];
+
+  var ta = new TA(makeCtorArg(["1", "2", "3", "4"]));
+  var options = {
+    get alphabet() {
+      calls.push("get options.alphabet");
+      return undefined;
+    },
+    get lastChunkHandling() {
+      calls.push("get options.lastChunkHandling");
+      return undefined;
+    },
+  };
+
+  assert.throws(TypeError, function() {
+    ta.setFromBase64("Zm9v", options);
+  });
+  assert.compareArray(calls, [], "Must verify mutability before reading arguments.");
+  assert.compareArray(ta, new TA(["1", "2", "3", "4"]), "Must not mutate contents.");
+}, [Uint8Array], ["immutable"]);

test/built-ins/Uint8Array/prototype/setFromHex/immutable-buffer.js

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+// Copyright (C) 2025 Richard Gibson. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-uint8array.prototype.setfromhex
+description: Throws a TypeError exception when the backing buffer is immutable
+info: |
+  Uint8Array.prototype.setFromHex ( string )
+  1. Let into be the this value.
+  2. Perform ? ValidateUint8Array(into).
+features: [TypedArray, uint8array-base64, immutable-arraybuffer]
+includes: [testTypedArray.js, compareArray.js]
+---*/
+
+testWithAllTypedArrayConstructors((TA, makeCtorArg) => {
+  var calls = [];
+
+  var ta = new TA(makeCtorArg(["1", "2", "3", "4"]));
+
+  assert.throws(TypeError, function() {
+    ta.setFromHex("666f6f");
+  });
+  assert.compareArray(calls, [], "Must verify mutability.");
+  assert.compareArray(ta, new TA(["1", "2", "3", "4"]), "Must not mutate contents.");
+}, [Uint8Array], ["immutable"]);