Add preliminary js upload

src/main/resources/static/js/customAssets.js

@@ -0,0 +1,55 @@
+const assetModal = document.getElementById("custom-asset-modal");
+const userSourceTextArea = document.getElementById("custom-asset-code");
+const formErrorWrapper = document.getElementById("custom-asset-error");
+const jsErrorTitle = document.getElementById("js-error-title");
+const jsErrorDetails = document.getElementById("js-error-details");
+
+function toggleCustomAssetModal(event) {
+    if (event !== undefined && event.target !== event.currentTarget) {
+        return;
+    }
+    if (assetModal.classList.contains("hidden")) {
+        assetModal.classList.remove("hidden");
+    } else {
+        assetModal.classList.add("hidden");
+    }
+}
+
+function submitCodeAsset(formEvent) {
+    formEvent.preventDefault();
+    const src = userSourceTextArea.value;
+    const error = getUserJavaScriptSourceError(src);
+    if (error) {
+        jsErrorTitle.textContent = error.title;
+        jsErrorDetails.textContent = error.details;
+        formErrorWrapper.classList.remove("hidden");
+        return false;
+    }
+    formErrorWrapper.classList.add("hidden");
+    jsErrorTitle.textContent = "";
+    jsErrorDetails.textContent = "";
+    return false;
+}
+
+function getUserJavaScriptSourceError(src) {
+    let ast;
+
+    try {
+        ast = acorn.parse(src, {
+            ecmaVersion: "latest",
+            sourceType: "script",
+        });
+    } catch (e) {
+        return { title: "Syntax Error", details: e.message };
+    }
+
+    const functionNames = ast.body.filter((node) => node.type === "FunctionDeclaration").map((node) => node.id.name);
+    if (!functionNames.includes("init")) {
+        return { title: "Missing function: init", details: "Your code must include a function named 'init'." };
+    }
+    if (!functionNames.includes("tick")) {
+        return { title: "Missing function: tick", details: "Your code must include a function named 'tick'." };
+    }
+
+    return undefined;
+}