fs.cp isn't available on stable nodejs@14 yet

build/run.js

@@ -196,7 +196,21 @@ commands.build.rust = async function (argv) {
         await checkWasmSize(paths.wasm.mainGz, limitMb)
     }
     // Copy WASM files from temporary directory to Webpack's `dist` directory.
-    await fs.cp(paths.wasm.root, paths.dist.wasm.root, { recursive: true })
+    await copyRecursively(paths.wasm.root, paths.dist.wasm.root, { recursive: true })
+}
+
+async function copyRecursively(src, dest, opts) {
+    var stats = await fs.stat(src);
+    var isDirectory = stats && stats.isDirectory();
+    if (isDirectory) {
+        await fs.mkdir(dest, opts)
+        let names = await fs.readdir(src)
+        for (let n of names) {
+            await copyRecursive(path.join(src, n), path.join(dest, n))
+        }
+    } else {
+        await fs.copyFile(src, dest)
+    }
 }
 
 // Check if compressed WASM binary exceeds the size limit.
@@ -630,7 +644,7 @@ async function downloadJsAssets() {
 
     const assetsArchive = await unzipper.Open.file(path.join(workdir, ideAssetsMainZip))
     await assetsArchive.extract({ path: workdir })
-    await fs.cp(unzippedAssets, jsLibAssets, { recursive: true })
+    await copyRecursively(unzippedAssets, jsLibAssets, { recursive: true })
     await fs.rm(workdir, { recursive: true, force: true })
 }