[RxJS] Creation operators: from, fromArray, fromPromise

The of() operator essentially converted a list of arguments to an Observable. Since arrays are often how we structure list of things in JavaScript, we should have a way of transforming arrays into Observables. This lesson teaches how you can convert from Arrays to Observables, from Promises to Observables, and from Iterators to Observables.

 

formArray:

var ary = [1,2,3];
var foo = Rx.Observable.fromArray(ary);


foo.subscribe(function (x) {
  console.log('next ' + x);
}, function (err) {
  console.log('error ' + err);
}, function () {
  console.log('done');
});

/*
"next 1"
"next 2"
"next 3"
"done"
*/

 

fromPromise:

var prom = fetch('https://null.jsbin.com');
var foo = Rx.Observable.fromPromise(prom);

foo.subscribe(function (x) {
  console.log('next ' + x.status);
}, function (err) {
  console.log('error ' + err);
}, function () {
  console.log('done');
});

/*
"next 204"
"done"
*/

 

from:

from() opreator can create observalbes according to what you passed in

=fromArray:

var ary = [1,2,3];
var foo = Rx.Observable.from(ary);

foo.subscribe(function (x) {
  console.log('next ' + x);
}, function (err) {
  console.log('error ' + err);
}, function () {
  console.log('done');
});

/*
"next 1"
"next 2"
"next 3"
"done"
*/

 

=fromPromiose

var foo = Rx.Observable.from(prom);

foo.subscribe(function (x) {
  console.log('next ' + x.status);
}, function (err) {
  console.log('error ' + err);
}, function () {
  console.log('done');
});

 

From iterator:

function* generator(){
  yield 10;
  yield 20;
  yield 30;
}

var iterator = generator();
var foo = Rx.Observable.from(iterator);

foo.subscribe(function (x) {
  console.log('next ' + x);
}, function (err) {
  console.log('error ' + err);
}, function () {
  console.log('done');
});

/*
"next 10"
"next 20"
"next 30"
"done"
*/