Why You Shouldn't Use Promises in Angular

While Promises can be useful for handling asynchronous operations in JavaScript, there are several reasons why they are not the preferred approach in Angular:


Angular uses a library called Zone.js to manage asynchronous operations, such as HTTP requests and timers. Zone.js patches the global objects for asynchronous APIs, such as setTimeout and XMLHttpRequest, to intercept their callbacks and automatically run change detection in Angular's application. However, Promises are not patched by Zone.js, which means that Angular may not be aware of changes made by Promise callbacks. This can result in unexpected behavior and can make it harder to debug the application.

Observable-based APIs

Angular provides Observable-based APIs for handling asynchronous operations, such as the HttpClient module for making HTTP requests. Observables have several advantages over Promises, including the ability to cancel requests, retry requests, and handle multiple values over time. Observables also integrate well with Angular's change detection system and are more efficient for handling streams of data.

Error handling

Promises have limited error-handling capabilities compared to Observables. With Promises, you can only handle one error using the catch method, whereas with Observables, you can handle multiple errors using the catchError operator. Additionally, Promises cannot be retried on error, whereas Observables can be retried using the retry operator.

Code readability

Promises can make code harder to read and understand, especially when chaining multiple promises together. This is because Promises use a chain of then-and-catch methods, which can be difficult to follow. Observables, on the other hand, use a series of operators that can be easily composed and combined to form complex streams of data.

In summary, while Promises can be useful for handling asynchronous operations in JavaScript, they are not the preferred approach in Angular. Observables are the recommended approach for handling asynchronous operations in Angular, due to their integration with Angular's change detection system, error handling capabilities, and ability to handle streams of data.