Support dots in identifiers

lib/sheet.js

@@ -37,6 +37,28 @@ const setCell = (target, prop, value) => {
     const options = { context: target.context };
     const script = metavm.createScript(prop, src, options);
     target.expressions.set(prop, script.exports);
+  } else if (prop.includes('.')) {
+    const rootKey = prop.slice(0, prop.indexOf('.'));
+    let targetKey = rootKey;
+
+    const proxyValue = new Proxy(
+      {},
+      {
+        get: (_, nextKey) => {
+          targetKey += `.${nextKey}`;
+
+          if (target.data.has(targetKey)) {
+            const value = target.data.get(targetKey);
+            targetKey = rootKey;
+            return value;
+          }
+          return proxyValue;
+        },
+      },
+    );
+
+    target.data.set(rootKey, proxyValue);
+    target.data.set(prop, value);
   } else {
     target.data.set(prop, value);
   }

test/unit.js

@@ -70,6 +70,21 @@ metatests.test('Correct cell values', async (test) => {
   test.end();
 });
 
+metatests.test('Non-table identifiers', async (test) => {
+  const sheet = new Sheet();
+  sheet.cells['item1.price'] = 100;
+  sheet.cells['item2.price'] = 200;
+  sheet.cells['item3.price'] = 300;
+  sheet.cells['total'] = '=item1.price + item2.price + item3.price';
+  test.strictSame(sheet.values['total'], 600);
+
+  sheet.cells['item3'] = 42;
+  test.strictSame(sheet.values['item3'], 42);
+  test.strictSame(sheet.values['total'], NaN);
+
+  test.end();
+});
+
 metatests.test('Prevent arbitrary js code execution', async (test) => {
   const sheet = new Sheet();