生成observable的函数
Rxjs中大概提供了32个函数，这些函数执行都返回Observable实例。
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用法示例
// RxJS v6+
import { from } from 'rxjs';
// 将数组作为值的序列发出
const arraySource = from([1, 2, 3, 4, 5]);
// 输出: 1,2,3,4,5
const subscribe = arraySource.subscribe(val => console.log(val));
源码
以fromArray为例
/**
* Subscribes to an ArrayLike with a subscriber
* @param array The array or array-like to subscribe to
*/
export const subscribeToArray = <T>(array: ArrayLike<T>) => (subscriber: Subscriber<T>) => {
for (let i = 0, len = array.length; i < len && !subscriber.closed; i++) {
subscriber.next(array[i]);
}
if (!subscriber.closed) {
subscriber.complete();
}
};
export function fromArray<T>(input: ArrayLike<T>, scheduler?: SchedulerLike) {
if (!scheduler) {
return new Observable<T>(subscribeToArray(input));
} else {
return new Observable<T>(subscriber => {
const sub = new Subscription();
let i = 0;
sub.add(scheduler.schedule(function () {
if (i === input.length) {
subscriber.complete();
return;
}
subscriber.next(input[i++]);
if (!subscriber.closed) {
sub.add(this.schedule());
}
}));
return sub;
});
}
}
