fromPromise does not exist on type Observable

UPDATE:

As of rxjs 6.0.0-beta.3, operators and observable creators should be imported from rxjs. Furthermore, fromPromise is not part of the public API anymore and its wrapped in the from method.

TL;DR;

UPDATE

For rxjs 6.0.0 use:

import { from } from 'rxjs';

var observableFromPromise =  from(promiseSrc);

UPDATE:

After the release of the pipeable operators in rxjs 5.5.x, the monkey patch approach is strongly discouraged. Consider to use the static method option.

Original answer

As of rxjs 5.4.x, fromPromise can be used as a static method or can be patched into the Observable prototype.

For the first, you can do the following:

import { fromPromise } from 'rxjs/observable/fromPromise';

var observableFromPromise = fromPromise(promiseSrc);

More info about this approach here

To do the second, you need to change your import statement:

import { Observable } from 'rxjs/Observable';
import 'rxjs/add/observable/fromPromise';

var observableFromPromise = Observable.fromPromise(promiseSrc);

More info about this approach here

Personally I would recommend the first one, considering that the 2nd approach is basically the 1rst, with the difference that the Observable prototype is changed.