js: fix Buffer constructor and Buffer.from (#16731)

test/js/node/test/parallel/test-buffer-sharedarraybuffer.js

@@ -0,0 +1,27 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+
+const sab = new SharedArrayBuffer(24);
+const arr1 = new Uint16Array(sab);
+const arr2 = new Uint16Array(12);
+arr2[0] = 5000;
+arr1[0] = 5000;
+arr1[1] = 4000;
+arr2[1] = 4000;
+
+const arr_buf = Buffer.from(arr1.buffer);
+const ar_buf = Buffer.from(arr2.buffer);
+
+assert.deepStrictEqual(arr_buf, ar_buf);
+
+arr1[1] = 6000;
+arr2[1] = 6000;
+
+assert.deepStrictEqual(arr_buf, ar_buf);
+
+// Checks for calling Buffer.byteLength on a SharedArrayBuffer.
+assert.strictEqual(Buffer.byteLength(sab), sab.byteLength);
+
+Buffer.from({ buffer: sab }); // Should not throw.