Catch more invalid data sources (#373)

* Catch more invalid data sources

* Update src/table.js

Co-authored-by: Mike Bostock <[email protected]>

---------

Co-authored-by: Mike Bostock <[email protected]>

Author: Annie Zhang

src/table.js

@@ -184,7 +184,7 @@ export async function loadDataSource(source, mode, name) {
 function sourceCache(loadSource) {
   const cache = new WeakMap();
   return (source, name) => {
-    if (!source) throw new Error("data source not found");
+    if (!source || typeof source !== "object") throw new Error("invalid data source");
     let promise = cache.get(source);
     if (!promise || (isDataArray(source) && source.length !== promise._numRows)) {
       // Warning: do not await here! We need to populate the cache synchronously.