> For the complete documentation index, see [llms.txt](https://www.learnrxjs.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://www.learnrxjs.io/learn-rxjs/operators/filtering/distinctuntilchanged.md).

# distinctUntilChanged

#### signature: `distinctUntilChanged(compare: function): Observable`

## Only emit when the current value is different than the last.

***

💡 distinctUntilChanged uses `===` comparison by default, object references must match!

💡 If you want to compare based on an object property, you can use [`distinctUntilKeyChanged`](/learn-rxjs/operators/filtering/distinctuntilkeychanged.md) instead!

***

### Why use `distinctUntilChanged`?

This operator stands guard, ensuring that you're not bombarded with repetitive information. Imagine if your best friend kept repeating the same story to you every time you met. It'd get old, right? The `distinctUntilChanged` operator does just that; it prevents subsequent identical emissions from an observable.

Think about a search bar on a website. As users type their queries, you don't want to send a server request for the same input value multiple times in a row, it would be redundant and inefficient. Here’s where `distinctUntilChanged` combined with [`debounceTime`](/learn-rxjs/operators/filtering/debouncetime.md) could shine. Imagine a user typing in a search term and then slightly hesitating before adding another letter. You might want to wait just a little bit (that’s (`debounceTime`)\[debouncetime.md] doing its magic) and then, before firing off a request, ensure the term is actually different than the previous one - this is where you can utilize `distinctUntilChanged`.

For example, if a user is searching for "apple" and they type "app" -> wait a bit -> "appl" -> backtrack to "app" -> type again "appl", without `distinctUntilChanged`, you might end up sending redundant requests. But with it, once "appl" is recognized as previously processed, it won't send the redundant search request again.

It's important to remember that **`distinctUntilChanged` compares the current value with the last emitted value**. It doesn’t keep a long history. So, if an observable emitted the values 1, 2, 2, 3, 3, 2 - you’d get 1, 2, 3, 2 in return. By default, it also uses simple equality to compare values. If you're working with objects or arrays, you might need to provide a custom comparison function to determine whether values are distinct.

In essence, when you're looking to filter out consecutive duplicate emissions from your observables, think of `distinctUntilChanged` as your go-to option.

### Examples

**Example 1: distinctUntilChanged with basic values**

( [StackBlitz](https://stackblitz.com/edit/typescript-bsb8mw?file=index.ts\&devtoolsheight=100) )

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

// only output distinct values, based on the last emitted value
const source$ = from([1, 1, 2, 2, 3, 3]);

source$
  .pipe(distinctUntilChanged())
  // output: 1,2,3
  .subscribe(console.log);
```

**Example 2: distinctUntilChanged with objects**

( [StackBlitz](https://stackblitz.com/edit/typescript-moe7mh?file=index.ts\&devtoolsheight=100) )

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

const sampleObject = { name: 'Test' };

//Objects must be same reference
const source$ = from([sampleObject, sampleObject, sampleObject]);

// only emit distinct objects, based on last emitted value
source$
  .pipe(distinctUntilChanged())
  // output: {name: 'Test'}
  .subscribe(console.log);
```

**Example 3: Using custom comparer function**

( [StackBlitz](https://stackblitz.com/edit/typescript-hzta27?file=index.ts\&devtoolsheight=100) )

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

// only output distinct values, based on the last emitted value
const source$ = from([
  { name: 'Brian' },
  { name: 'Joe' },
  { name: 'Joe' },
  { name: 'Sue' }
]);

source$
  // custom compare for name
  .pipe(distinctUntilChanged((prev, curr) => prev.name === curr.name))
  // output: { name: 'Brian }, { name: 'Joe' }, { name: 'Sue' }
  .subscribe(console.log);
```

### Related Recipes

* [Lockscreen](/learn-rxjs/recipes/lockscreen.md)
* [Save Indicator](/learn-rxjs/recipes/save-indicator.md)
* [Type Ahead](/learn-rxjs/recipes/type-ahead.md)

### Additional Resources

* [distinctUntilChanged](https://rxjs.dev/api/operators/distinctUntilChanged) 📰 - Official docs
* [Filtering operator: distinct and distinctUntilChanged](https://egghead.io/lessons/rxjs-filtering-operators-distinct-and-distinctuntilchanged?course=rxjs-beyond-the-basics-operators-in-depth) 🎥 💵 - André Staltz

***

> 📁 Source Code: <https://github.com/ReactiveX/rxjs/blob/master/packages/rxjs/src/internal/operators/distinctUntilChanged.ts>


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation by asking a question.

Perform an HTTP GET request on the following URL with the `ask` and `goal` query parameters:

```
GET https://www.learnrxjs.io/learn-rxjs/operators/filtering/distinctuntilchanged.md?ask=<question>&goal=<user_goal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is what the user is ultimately trying to achieve, the reason they need the answer. Sharing it helps GitBook give you a better, more relevant answer. A goal is most helpful when it describes the outcome the user wants rather than restating the question. For example, with `ask=how do I create an API token`, a goal like `automate deployments from our CI pipeline` lets GitBook tailor the answer to that use case.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.