Throw error if onCancel is called after promise settlement (#18)

sindresorhus · Mar 31, 2019 · c4ebb36 · c4ebb36
1 parent 8746e2a
commit c4ebb36
Showing 1 changed file with 4 additions and 0 deletions.
diff --git a/index.js b/index.js
@@ -41,6 +41,10 @@ class PCancelable {
 			};
 
 			const onCancel = handler => {
+				if (!this._isPending) {
+					throw new Error('The `onCancel` handler was attached after the promise settled.');
+				}
+
 				this._cancelHandlers.push(handler);
 			};