from

• 语法:

public static from(ish: ObservableInput<T>, scheduler: Scheduler): Observable<T>

• 功能：将一个数组、类数组(字符串也可以)，Promise、可迭代对象，类可观察对象、转化为一个Observable

可将几乎所有的东西转化一个可观察对象

eg:

// 数组=>Observable
var array = [10, 20, 30];
var result = Rx.Observable.from(array);
result.subscribe(x => console.log(x));

// 无限迭代对象=>Observable
function* generateDoubles(seed) {
  var i = seed;
  while (true) {
    yield i;
    i = 2 * i; // double it
  }
}

var iterator = generateDoubles(3);
var result = Rx.Observable.from(iterator).take(10);
result.subscribe(x => console.log(x));

f-eg

function* generateDoubles(seed) {
  var i = seed;
  while (true) {
    yield i;
    i = 2 * i; // double it
  }
}

var iterator = generateDoubles(3);
var result = Rx.Observable.from(iterator).take(10);
result.subscribe(x => console.log(x));

var s = new Set(["foo", window]);

Rx.Observable.from(s).subscribe(
  x => console.log(`onNext: ${x}`),
  e => console.log(`onError: ${e}`),
  () => console.log('onCompleted'));

// => onNext: foo
// => onNext: window
// => onCompleted