fix: throw helpful error if passing function to createParser()

src/parse.ts

@@ -23,6 +23,12 @@ function noop(_arg: unknown) {
  * @public
  */
 export function createParser(callbacks: ParserCallbacks): EventSourceParser {
+  if (typeof callbacks === 'function') {
+    throw new TypeError(
+      '`callbacks` must be an object, got a function instead. Did you mean `{onEvent: fn}`?',
+    )
+  }
+
   const {onEvent = noop, onError = noop, onRetry = noop, onComment} = callbacks
 
   let incompleteLine = ''

test/parse.test.ts

@@ -417,3 +417,12 @@ test('calls onError when the stream is invalid (no field separator)', async () =
     line: 'Well, this is not what I expected',
   })
 })
+
+test('passing a function to `createParser` will throw with helpful error', () => {
+  expect(() => {
+    // @ts-expect-error Should not allow a function, typing-wise
+    createParser(() => null)
+  }).toThrowError(
+    '`callbacks` must be an object, got a function instead. Did you mean `{onEvent: fn}`?',
+  )
+})