feat: add ability to create arrays with capacity for __newArray in loader

lib/loader/index.d.ts

@@ -92,7 +92,7 @@ export interface ASUtil {
   /** Allocates a new ArrayBuffer in the module's memory and returns a reference (pointer) to it. */
   __newArrayBuffer(buf: ArrayBuffer): number;
   /** Allocates a new array in the module's memory and returns a reference (pointer) to it. */
-  __newArray(id: number, values: ArrayLike<number>): number;
+  __newArray(id: number, valuesOrCapacity?: Array<number> | ArrayBufferView | number): number;
 
   /** Allocates an instance of the class represented by the specified id. */
   __new(size: number, id: number): number;

lib/loader/index.js

@@ -195,10 +195,12 @@ function postInstantiate(extendedExports, instance) {
   }
 
   /** Allocates a new array in the module's memory and returns its pointer. */
-  function __newArray(id, values) {
+  function __newArray(id, valuesOrCapacity = 0) {
+    const input = valuesOrCapacity;
     const info = getArrayInfo(id);
     const align = getValueAlign(info);
-    const length = values.length;
+    const isArrayLike = typeof input !== "number";
+    const length = isArrayLike ? input.length : input;
     const buf = __new(length << align, info & STATICARRAY ? id : ARRAYBUFFER_ID);
     let result;
     if (info & STATICARRAY) {
@@ -214,14 +216,16 @@ function postInstantiate(extendedExports, instance) {
       if (info & ARRAY) U32[arr + ARRAY_LENGTH_OFFSET >>> 2] = length;
       result = arr;
     }
-    const view = getView(align, info & VAL_SIGNED, info & VAL_FLOAT);
-    if (info & VAL_MANAGED) {
-      for (let i = 0; i < length; ++i) {
-        const value = values[i];
-        view[(buf >>> align) + i] = value;
+    if (isArrayLike) {
+      const view = getView(align, info & VAL_SIGNED, info & VAL_FLOAT);
+      const start = buf >>> align;
+      if (info & VAL_MANAGED) {
+        for (let i = 0; i < length; ++i) {
+          view[start + i] = input[i];
+        }
+      } else {
+        view.set(input, start);
       }
-    } else {
-      view.set(values, buf >>> align);
     }
     return result;
   }

lib/loader/tests/index.js

@@ -186,6 +186,20 @@ function test(file) {
     assert.deepStrictEqual(exports.__getArray(ref), arr);
   }
 
+  // should be able to create empty arrays
+  {
+    let ref = exports.__newArray(exports.ARRAYI32_ID);
+    assert(exports.__instanceof(ref, exports.ARRAYI32_ID));
+    assert.deepStrictEqual(exports.__getArray(ref), []);
+  }
+
+  // should be able to create arrays with capacity
+  {
+    let ref = exports.__newArray(exports.ARRAYI32_ID, 32);
+    assert(exports.__instanceof(ref, exports.ARRAYI32_ID));
+    assert.strictEqual(exports.__getArray(ref).length, 32);
+  }
+
   // should be able to work with normal arrays
   {
     let arr = [1, 2, 3, 4, 5];