What is the difference between Promises and Observables?

Question

What is the difference between Promise and Observable in Angular?

An example on each would be helpful in understanding both the cases. In w

Answer 1

Even though this answer is late, i have summarized the differences below,

Observable:

1. Observable is just a function that takes an observer and returns a function Observer: an object with next, error.
2. Observer allows to subscribe/unsubscribe to its data stream, emit next value to the observer, notify the observer about errors and inform the observer about the stream completion
3. Observer provides a function to handle next value,errors and end of stream(ui events,http responses,data with web sockets).
4. Works with multiple values over time
5. It is cancel-able/retry-able and supports operators such as map,filter,reduce etc.
6. Creating an Observable can be -Observable.create() - returns Observable that can invoke methods on -Observer Observable.from() - converts an array or iterable into -Observable Observable.fromEvent() - converts an event into Observable -Observable.fromPromise() - converts a Promise into Observable -Observable.range() - returns a sequence of integers in the specified range

Promise:

1. A promise represents a task that will finish in the future;

2. Promises become resolved by a value;

3. Promises get rejected by exceptions;

4. Not cancellable and it returns a single value

5. A promise expose a function (then)

   -then returns a new promise;

   -allows for the attachment of that will be executed based on state;

   -handlers are guaranteed to execute in order attached;