Refactor content type check for response handling

Author: jonrohan

src/include-fragment-element.ts

@@ -237,10 +237,6 @@ export class IncludeFragmentElement extends HTMLElement {
       if (response.status !== 200) {
         throw new Error(`Failed to load resource: the server responded with a status of ${response.status}`)
       }
-      const ct = response.headers.get('Content-Type')
-      if (!isWildcard(this.accept) && (!ct || !ct.includes(this.accept ? this.accept : 'text/html'))) {
-        throw new Error(`Failed to load resource: expected ${this.accept || 'text/html'} but was ${ct}`)
-      }
 
       const responseText: string = await response.text()
       let data: string | CSPTrustedHTMLToStringable = responseText
@@ -259,6 +255,10 @@ export class IncludeFragmentElement extends HTMLElement {
       // the `load()` promise to resolve _before_ these
       // events are fired.
       this.#task(['error', 'loadend'], error as Error)
+      const ct = response.headers.get('Content-Type')
+      if (!isWildcard(this.accept) && (!ct || !ct.includes(this.accept ? this.accept : 'text/html'))) {
+        throw new Error(`Failed to load resource: expected ${this.accept || 'text/html'} but was ${ct}`)
+      }
       throw error
     }
   }