takeWhile

signature: takeWhile(predicate: function(value, index): boolean): Observable

Emit values until provided expression is false.

Examples

Example 1: Take values under limit

( jsBin | jsFiddle )

//emit 1,2,3,4,5
const source = Rx.Observable.of(1,2,3,4,5);
//allow values until value from source is greater than 4, then complete
const example = source.takeWhile(val => val <= 4);
//output: 1,2,3,4
const subscribe = example.subscribe(val => console.log(val));
Example 2: Difference between takeWhile() and filter()

( jsBin | jsFiddle )

// emit 3, 3, 3, 9, 1, 4, 5, 8, 96, 3, 66, 3, 3, 3
const source = Rx.Observable.of(3, 3, 3, 9, 1, 4, 5, 8, 96, 3, 66, 3, 3, 3);

// allow values until value from source equals 3, then complete
// output: [3, 3, 3]
source
 .takeWhile(it => it === 3 )
 .subscribe(val => console.log('takeWhile', val));

// output: [3, 3, 3, 3, 3, 3, 3]
source
 .filter(it => it === 3)
 .subscribe(val => console.log('filter', 3));

Additional Resources


:file_folder: Source Code: https://github.com/ReactiveX/rxjs/blob/master/src/operator/takeWhile.ts

results matching ""

    No results matching ""