from
- 签名: from(ish: ObservableInput, mapFn: function, thisArg: any, scheduler: Scheduler): Observable
将数组、promise 或迭代器转换成 observable 。
- 示例
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from

签名: `from(ish: ObservableInput, mapFn: function, thisArg: any, scheduler: Scheduler): Observable`

将数组、promise 或迭代器转换成 observable 。

对于数组和迭代器，所有包含的值都会被作为序列发出！

此操作符也可以用来将字符串作为字符的序列发出！

示例

示例 1: 数组转换而来的 observable

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

示例 2: promise 转换而来的 observable

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jsFiddle )

import { from } from 'rxjs/observable/from';
// 发出 promise 的结果
const promiseSource = from(new Promise(resolve => resolve('Hello World!')));
// 输出: 'Hello World'
const subscribe = promiseSource.subscribe(val => console.log(val));

示例 3: 集合转换而来的 observable

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import { from } from 'rxjs/observable/from';
// 使用 js 的集合
const map = new Map();
map.set(1, 'Hi');
map.set(2, 'Bye');
const mapSource = from(map);
// 输出: [1, 'Hi'], [2, 'Bye']
const subscribe = mapSource.subscribe(val => console.log(val));

示例 4: 字符串转换而来的 observable

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jsFiddle )

import { from } from 'rxjs/observable/from';
// 将字符串作为字符序列发出
const source = from('Hello World');
// 输出: 'H','e','l','l','o',' ','W','o','r','l','d'
const subscribe = source.subscribe(val => console.log(val));