API / rxjs/operators

find

Emits only the first value emitted by the source Observable that meets some condition.

find<T>(predicate: (value: T, index: number, source: Observable<T>) => boolean, thisArg?: any): OperatorFunction<T, T | undefined>

Parameters

predicate

A function called with each item to test for condition matching.
thisArg

Optional. Default is undefined.

An optional argument to determine the value of this in the predicate function.

Returns

OperatorFunction<T, T | undefined>: An Observable of the first item that matches the condition.

Description

Finds the first value that passes some test and emits that.

find searches for the first item in the source Observable that matches the specified condition embodied by the predicate, and returns the first occurrence in the source. Unlike first, the predicate is required in find, and does not emit an error if a valid value is not found.

Example

Find and emit the first click that happens on a DIV element

import { fromEvent } from 'rxjs'; import { find } from 'rxjs/operators'; const clicks = fromEvent(document, 'click'); const result = clicks.pipe(find(ev => ev.target.tagName === 'DIV')); result.subscribe(x => console.log(x));

See Also