Rx.Observable.from(iterable, [mapFn], [thisArg], [scheduler])

从Array创建一个Observable，参数也可以是一个类数组的对象，一个Promise，一个可迭代对象或一个Observable类对象。

参数

1. iterable (Array | Arguments | Iterable): 类数组或可迭代对象
2. [mapFn] (Function): 应用到第一个参数的映射函数
3. [thisArg] (Any): 提供映射函数上下文
4. [scheduler=Rx.Scheduler.currentThread] (Scheduler): 枚举输入序列的调度器

返回值

(Observable): 通过给定的可迭代序列生成的observable.

例

Array-like object (arguments) to Observable

function f() {
  return Rx.Observable.from(arguments);
}

f(1, 2, 3).subscribe(
  x => console.log(`onNext: ${x}`),
  e => console.log(`onError: ${e}`),
  () => console.log('onCompleted'));

// => onNext: 1
// => onNext: 2
// => onNext: 3
// => onCompleted

Set

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

Map

var m = new Map([[1, 2], [2, 4], [4, 8]]);

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

// => onNext: [1, 2]
// => onNext: [2, 4]
// => onNext: [4, 8]
// => onCompleted

String

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

// => onNext: f
// => onNext: o
// => onNext: o
// => onCompleted

Array

Rx.Observable.from([1, 2, 3], x => x + x).subscribe(
  x => console.log(`onNext: ${x}`),
  e => console.log(`onError: ${e}`),
  () => console.log('onCompleted'));

// => onNext: 2
// => onNext: 4
// => onNext: 6
// => onCompleted

Generate a sequence of numbers

Rx.Observable.from({length: 5}, (v, k) => k).subscribe(
  x => console.log(`onNext: ${x}`),
  e => console.log(`onError: ${e}`),
  () => console.log('onCompleted'));

// => onNext: 0
// => onNext: 1
// => onNext: 2
// => onNext: 3
// => onNext: 4
// => onCompleted