Use DataView to access WebAssembly memory (#37)

Accompanying mdn/content#33960 --------- Co-authored-by: Hamish Willee <[email protected]>
mdn · Jun 7, 2024 · 1b53615 · 1b53615
1 parent cf86061
commit 1b53615
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Showing 2 changed files with 11 additions and 10 deletions.
diff --git a/js-api-examples/memory.html b/js-api-examples/memory.html
@@ -11,14 +11,14 @@
     <script>
       const memory = new WebAssembly.Memory({
         initial: 10,
-        maximum: 100
+        maximum: 100,
       });
-
-      WebAssembly.instantiateStreaming(fetch("memory.wasm"), { js: { mem: memory } })
-      .then(obj => {
-        const summands = new Uint32Array(memory.buffer);
+      WebAssembly.instantiateStreaming(fetch("memory.wasm"), {
+        js: { mem: memory },
+      }).then((obj) => {
+        const summands = new DataView(memory.buffer);
         for (let i = 0; i < 10; i++) {
-          summands[i] = i;
+          summands.setUint32(i * 4, i, true); // WebAssembly is little endian
         }
         const sum = obj.instance.exports.accumulate(0, 10);
         console.log(sum);

diff --git a/understanding-text-format/memory-export.html b/understanding-text-format/memory-export.html
@@ -10,11 +10,12 @@
     <script>
       WebAssembly.instantiateStreaming(fetch("memory-export.wasm")).then(
         (object) => {
-          const values = new Uint32Array(object.instance.exports.memory.buffer);
+          const values = new DataView(object.instance.exports.memory.buffer);
+          let sum = 0;
           // views only the first ten elements of the Wasm memory
-          const summands = values.subarray(0, 10);
-          // sums the first ten elements
-          const sum = summands.reduce((sum, summand) => sum + summand);
+          for (let i = 0 ; i < 10; i++) {
+            sum += values.getUint32(i * 4, true);
+          }
           console.log(sum);
         }
       );