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NgZone optimizations

In order to provide a seamless integration, if not configured otherwise, rxLet will process any updates inside of NgZone.

However, this is a potential source of negative impacts on the performance of your application. Since the updates processed by rxLet will most likely happen in batches, every batch will trigger one NgZone cycle, leading to unnecessary work as well as possible over renderings of other components.

There are two ways to opt-out from NgZone.

patchZone Input

*rxLet can be configured to create views inside of NgZone with the patchZone flag.

Take a look at the following example:

selector: 'app-root',
template: `
<!-- clickedHeroName won't get updated due to `NgZone` not noticing the click -->
{{ clickedHeroName }}
<!-- click runs out of `NgZone` -->
<button *rxLet="heroes$; let hero; patchZone: false"
{{ }}
export class AppComponent {
clickedHeroName = '';

heroClicked(hero: Hero) {
// this will run out of `NgZone` and probably not update the DOM
this.clickedHeroName =;


You can also set the patchZone config globally by providing a RX_RENDER_STRATEGIES_CONFIG. See more about configuration under render strategies especially the section usage-in-the-template

providers: [{
useValue: {
patchZone: false // this applies to all letDirectives