ng-observe
v1.1.0
Published
Angular reactivity streamlined...
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Angular reactivity streamlined...
Why?
- Unlike AsyncPipe, you can use it in component classes and even in directives.
- Feels more reactive than unsubscribing on destroy (be it handled by a decorator, triggered by a subject, or done by a direct call in the lifecycle hook).
- Reduces the complexity of working with streams.
- Works in zoneless apps. (v1.1.0+)
How it works
- Extracts emitted value from observables.
- Marks the component for change detection.
- Leaves no subscription behind.
- Clears old subscriptions and creates new ones at each execution if used in getters, setters or methods.
How to use
Install the package, and you are good to go. No module import is necessary.
npm install ng-observe
...or...
yarn add ng-observe
Example
We can subscribe to a stream with the AsyncPipe
in component templates, but we can't use it in component or directive classes.
@Component({
template: '{{ fooBar$ | async }}',
})
class DemoComponent {
foo$ = of('foo');
get fooBar$() {
return foo$.pipe(map(val => val + 'bar'));
}
}
With ng-observe, we don't need to pipe the stream.
import { OBSERVE, OBSERVE_PROVIDER, ObserveFn } from 'ng-observe';
@Component({
template: '{{ fooBar }}',
providers: [OBSERVE_PROVIDER],
})
class DemoComponent {
foo = this.observe(of('foo'));
get fooBar() {
return this.foo.value + 'bar';
}
constructor(@Inject(OBSERVE) private observe: ObserveFn) {}
}
You can see other examples at links below:
Important Note: Do not destructure a collection created by the
ObserveFn
. Otherwise, the reactivity will be lost. UsetoValue
ortoValues
to convert elements of the collection to instances ofObserved
instead.
You can read this Medium article to learn about what the motivation behind ng-observe is.
API
OBSERVE_PROVIDER
To use ng-observe in your components and directives, add OBSERVE_PROVIDER
to providers array in metadata.
ObserveFn
This function is used to extract a single stream's value. You can inject it via the OBSERVE
injection token.
import { OBSERVE, OBSERVE_PROVIDER, ObserveFn } from 'ng-observe';
@Component({
template: '{{ foo.value }}',
providers: [OBSERVE_PROVIDER],
})
class Component {
foo = this.observe(of('foo'));
constructor(@Inject(OBSERVE) private observe: ObserveFn) {}
}
You can extract multiple streams' value too.
import { OBSERVE, OBSERVE_PROVIDER, ObserveFn } from 'ng-observe';
@Component({
template: '{{ state.foo }} {{ state.bar }}',
providers: [OBSERVE_PROVIDER],
})
class Component {
state = this.observe({ foo: of('foo'), bar: of('bar') });
constructor(@Inject(OBSERVE) private observe: ObserveFn) {}
}
It works with arrays as well.
import { OBSERVE, OBSERVE_PROVIDER, ObserveFn } from 'ng-observe';
@Component({
template: '{{ state[0] }} {{ state[1] }}',
providers: [OBSERVE_PROVIDER],
})
class Component {
state = this.observe([of('foo'), of('bar')]);
constructor(@Inject(OBSERVE) private observe: ObserveFn) {}
}
ObserveService
You can call ObserveService
's value
and collection
methods explicitly instead of ObserveFn
. This offers a very slight (ignorable in most cases) performance improvement.
import { ObserveService } from 'ng-observe';
@Component({
template: '{{ foo.value }} {{ state[0] }} {{ state[1] }}',
providers: [ObserveService],
})
class Component {
foo = this.observe.value(of('foo'));
state = this.observe.collection([of('foo'), of('bar')]);
constructor(private observe: ObserveService) {}
}
Observed
ObserveFn
infers types for you, but if you want to assign an observed value later, you can use Observed
class for type annotation.
import { OBSERVE, OBSERVE_PROVIDER, Observed } from 'ng-observe';
@Component({
template: '{{ foo.value }}',
providers: [OBSERVE_PROVIDER],
})
class Component {
foo: Observed<string>;
constructor(@Inject(OBSERVE) private observe: ObserveFn) {
this.foo = this.observe(of('foo'));
}
}
toValue
toValue
converts an element in the collection to a reactive observed value. Returns an instance of the Observed
class.
import { OBSERVE, OBSERVE_PROVIDER, Observed, ObserveFn, toValue } from 'ng-observe';
@Component({
template: '{{ foo.value }} {{ bar.value }}',
providers: [OBSERVE_PROVIDER],
})
class Component {
foo: Observed<string>;
bar: Observed<string>;
constructor(@Inject(OBSERVE) private observe: ObserveFn) {
const state = this.observe({ foo: of('foo'), bar: of('bar') });
this.foo = toValue(state, 'foo');
this.bar = toValue(state, 'bar');
}
}
toMappedValue
You can use toMappedValue
to get a reactive observed value mapped from the collection. Returns an instance of the Observed
class.
import { OBSERVE, OBSERVE_PROVIDER, Observed, ObserveFn, toMappedValue } from 'ng-observe';
@Component({
template: '{{ fooBar.value }}',
providers: [OBSERVE_PROVIDER],
})
class Component {
fooBar: Observed<string>;
constructor(@Inject(OBSERVE) private observe: ObserveFn) {
const state = this.observe({ foo: of('foo'), bar: of('bar') });
this.fooBar = toMappedValue(state, ({ foo, bar }) => `${foo} ${bar}`);
}
}
toValues
toValues
converts all elements in collection to reactive observed values. Returns an array/object the indices/keys of which will be the same with the input collection. Each element will be an instance of the Observed
class.
import { OBSERVE, OBSERVE_PROVIDER, Observed, ObserveFn, toValues } from 'ng-observe';
@Component({
template: '{{ foo.value }} {{ bar.value }}',
providers: [OBSERVE_PROVIDER],
})
class Component {
foo: Observed<string>;
bar: Observed<string>;
constructor(@Inject(OBSERVE) private observe: ObserveFn) {
const state = this.observe({ foo: of('foo'), bar: of('bar') });
const { foo, bar } = toValues(state);
this.foo = foo;
this.bar = bar;
}
}
isCollection
Collections observed by ng-observe are plain arrays or objects, but you can detect them with isCollection
function. It returns true
when input is an observed collection, and false
when not.
import { isCollection, OBSERVE, OBSERVE_PROVIDER, ObserveFn } from 'ng-observe';
@Component({
template: '<!-- not important for this example -->',
providers: [OBSERVE_PROVIDER],
})
class Component {
constructor(@Inject(OBSERVE) private observe: ObserveFn) {
const state = this.observe({ foo: of('foo'), bar: of('bar') });
console.log(isCollection(state)); // true
}
}