distinctUntilChanged

函数签名: distinctUntilChanged(compare: function): Observable

只有当当前值与之前最后一个值不同时才将其发出。

distinctUntilChanged 默认使用 === 进行比较, 对象引用必须匹配！

示例

示例 1: 使用基础值进行 distinctUntilChanged

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { from } from 'rxjs';
import { distinctUntilChanged } from 'rxjs/operators';

// 基于最新发出的值进行比较，只输出不同的值
const myArrayWithDuplicatesInARow = from([1, 1, 2, 2, 3, 1, 2, 3]);

const distinctSub = myArrayWithDuplicatesInARow
  .pipe(distinctUntilChanged())
  // 输出: 1,2,3,1,2,3
  .subscribe(val => console.log('DISTINCT SUB:', val));

const nonDistinctSub = myArrayWithDuplicatesInARow
  // 输出 : 1,1,2,2,3,1,2,3
  .subscribe(val => console.log('NON DISTINCT SUB:', val));

示例 2: 使用对象进行 distinctUntilChanged

( StackBlitz | jsBin | jsFiddle )

// RxJS v6+
import { from } from 'rxjs';
import { distinctUntilChanged } from 'rxjs/operators';

const sampleObject = { name: 'Test' };
// 对象必须有相同的引用
const myArrayWithDuplicateObjects = from([
  sampleObject,
  sampleObject,
  sampleObject
]);
// 基于最新发出的值进行比较，只输出不同的对象
const nonDistinctObjects = myArrayWithDuplicateObjects
  .pipe(distinctUntilChanged())
  // 输出: 'DISTINCT OBJECTS: {name: 'Test'}
  .subscribe(val => console.log('DISTINCT OBJECTS:', val));

其他资源

• distinctUntilChanged :newspaper: - 官方文档
• 过滤操作符: distinct 和 distinctUntilChanged :video_camera: :dollar: - André Staltz

源码: https://github.com/ReactiveX/rxjs/blob/master/src/internal/operators/distinctUntilChanged.ts