Update README with Awaitable

README.md

@@ -95,12 +95,14 @@ const metadata = parquetMetadata(arrayBuffer)
 
 ### AsyncBuffer
 
-Hyparquet accepts argument `file` of type `AsyncBuffer` which is like a js `ArrayBuffer` but the `slice` method returns `Promise<ArrayBuffer>`.
+Hyparquet accepts argument `file` of type `AsyncBuffer` which is like a js `ArrayBuffer` but the `slice` method can return `Promise<ArrayBuffer>`.
+You can pass an `ArrayBuffer` anywhere that an `AsyncBuffer` is expected, if you have the entire file in memory.
 
 ```typescript
+type Awaitable<T> = T | Promise<T>
 interface AsyncBuffer {
   byteLength: number
-  slice(start: number, end?: number): Promise<ArrayBuffer>
+  slice(start: number, end?: number): Awaitable<ArrayBuffer>
 }
 ```
 

test/utils.test.js

@@ -166,7 +166,8 @@ describe('asyncBufferFromUrl', () => {
       })
     })
 
-    expect(asyncBufferFromUrl({ url: 'https://example.com' })).rejects.toThrow('fetch head failed 401')
+    await expect(asyncBufferFromUrl({ url: 'https://example.com' }))
+      .rejects.toThrow('fetch head failed 401')
 
     const buffer = await asyncBufferFromUrl({ url: 'https://example.com', requestInit: { headers: { Authorization: 'Bearer token' } } } )
     expect(buffer.byteLength).toBe(1024)
@@ -195,11 +196,11 @@ describe('asyncBufferFromUrl', () => {
     })
 
     const noHeaders = await asyncBufferFromUrl({ url: 'https://example.com', byteLength: 1024 })
-    expect(noHeaders.slice(0, 100)).rejects.toThrow('fetch failed 401')
+    await expect(noHeaders.slice(0, 100)).rejects.toThrow('fetch failed 401')
 
     const withHeaders = await asyncBufferFromUrl({ url: 'https://example.com', byteLength: 1024, requestInit: { headers: { Authorization: 'Bearer token' } } } )
-    expect (await withHeaders.slice(0, 100)).toBe(mockArrayBuffer)
+    await expect(withHeaders.slice(0, 100)).resolves.toBe(mockArrayBuffer)
 
-    expect (withHeaders.slice(0, 10)).rejects.toThrow('fetch failed 404')
+    await expect(withHeaders.slice(0, 10)).rejects.toThrow('fetch failed 404')
   })
 })