This commit exposes the new `output()` API with numerous benefits:
- Symmetrical API to `input()`, `model()` etc.
- Fixed types for `EventEmitter.emit`— current `emit` method of
`EventEmitter` is broken and accepts `undefined` via `emit(value?: T)`
- Removal of RxJS specific concepts from outputs. error channels,
completion channels etc. We now have a simple consistent
interface.
- Automatic clean-up of subscribers upon directive/component destory-
when subscribed programmatically.
```ts
@Directive({..})
export class MyDir {
nameChange = output<string>(); // OutputEmitterRef<string>
onClick = output(); // OutputEmitterRef<void>
}
```
Note: RxJS custom observable cases will be handled in future commits via
explicit helpers from the interop.
PR Close#54650
Adds support for model inputs in the framework. `model()` returns a writable signal that implicitly defines a input/output pair that can be used either in two-way bindings to keep two values in sync or by binding individually to the input and output. When the value of the `model` changes, it will emit an event with the current value.
Furthermore, these changes expand two-way bindings to accept `WritableSignal`. This will make it easier to transition existing code to signals in a backwards-compatible way.
Example:
```ts
@Directive({
selector: 'counter',
standalone: true,
host: {
'(click)': 'increment()',
}
})
export class Counter {
value = model(0);
increment(): void {
this.value.update(current => current + 1);
}
}
@Component({
template: `<counter [(value)]="count"/> The current count is: {{count()}}`,
})
class App {
count = signal(0);
}
```
PR Close#54252
This commit introduces the `output()` function and corresponding
runtime code.
In practice, `output()` will defer to `EventEmitter` as outlined in the
RFC, but we are considering limiting the type to a minimal version that
is not coupled with RxJS, less complex, and also has better type safety
around emitting of values.
E.g. currently `EventEmitter.emit` can always be called without
any value, even though the output may be typed to always pass around
values of type `T`. This could cause subtle and confusing bugs.
PR Close#54217
This commit separates `InputSignal` for input signals with transforms.
The reason being that most of the time, signal inputs are not using
transforms and the generics are rather confusing.
Especially for users with inferred types displayed in their IDEs, the
input signal types are seemingly complex, even if no transform is used.
For this reason, we are introducing a new type called
`InputSignalWithTransform`. This type will be used for inputs with
transforms, while non-transform inputs just use `InputSignal`.
A notable fact is that `InputSignal` extends `InputSignalWithTransform`,
with the "identity transform". i.e. there is no transform. This allows
us to share the code for input signals. In practice, we don't expect
users to pass around `InputSignal`'s anyway.
PR Close#54053
Enables signal inputs for existing Zone based components.
This is a next step we are taking to bring signal inputs earlier to the Angular community.
The goal is to enable early access for the ecosystem to signal inputs, while we are continuing
development of full signal components as outlined in the RFC. This will allow the ecosystem
to start integrating signals more deeply, prepare for future migrations, and improves code quality
and DX for existing components (especially for OnPush).
Based on our work on full signal components, we've gathered more information and learned
new things. We've improved the API by introducing a way to intuitively declare required inputs,
as well as improved the API around initial values. We even support non-primitive initial values
as the first argument to the `input` function now.
```ts
@Directive({..})
export class MyDir {
firstName = input<string>(); // string|undefined
lastName = input.required<string>(); // string
age = input(0); // number
```
PR Close#53872
This commit adds the last remaining piece for signal input
type-checking. Bound values to signal inputs are already checked
properly at this point, but inference of generic directive/component
types through their inputs is not implemented.
This commit fixes this. To achieve this, there are a couple of potential
solutions. The generics of a directive are inferred based on input
value expressions using a so-called type constructor. The constructor
looks something like this:
```
const _ctor = <T>(v: Pick<Dir<T>, 'input1', 'input2'>) => Dir<T>;
_ctor({input1: expr1, input2: expr2});
```
This works very well for non-signal inputs where the class member is
directly holding the input values. For signal inputs, this does NOT
work because the class member will actually hold the `InputSignal`
instance. There are a couple of solutions to this:
1. Calling `_ctor` with an `InputSignal<typeof value>`
2. Converting the `_ctor` input signal fields to their write types
(unwrapping the input signals).
We've decided to go with the second option as TypeScript is very
sensitive with assignments and its checks. i.e. co-variance,
contravariance or bivariance. Semantically it makes more sense to unwrap
the input signal "write type" directly and "assign to it". This is safer
and conceptually also easier to follow. A type constructor continues to
only receive the "expresison values". This simplifies code as well.
It's worth noting that the unwrapping as per option 2 also comes at a
cost. We need to be able to generate imports in type constructors. This
was not possible until the previous commit because inline type constructors
did not have an associated type-check block `Environment` and we were
missing access to expression translation and correct import generation.
Overall, solution 2 is now implemented as works as expected. This commit
adds additional unit tests to ensure this.
PR Close#53521
This commit introduces the initial type-checking for signal inputs.
To enable type-checking od signal inputs, there are a couple of tricks
needed. It's not trivial as it would look like at first glance.
Initial attempts could have been to generate additional statements in
type-checking blocks for signal inputs to simply call a method like
`InputSignal#applyNewValue`. This would seem natural, as it would match
what will happen at runtime, but this would break the language-service
auto completion in a highly subtle way. Consider the case where multiple
directives match the same input. Consider the directives have some
overlap in accepted input values, but they also have distinct diverging
values, like:
```ts
class DirA {
value = input<'apple'|'shared'>();
}
class DirB {
value = input<'orange'|'shared'>();
}
```
In such cases, auto completion for the binding expression should suggest
the following values: `apple`, `shared`, `orange` and `undefined`.
The language service achieves this by getting completions in the
type-check block where the user expression would live. This BREAKS if
we'd have multiple places where the expression from the user is used.
Two different places, or more, surface additional problems with
diagnostic collection. Previously diagnostics would surface the union
type of allowed values, but with multiple places, we'd have to work with
potentially 1+ diagnostics. This is non-ideal.
Another important consideration is test coverage. It might sound
problematic to consider the existing test infrastructure as relevant,
but in practice, we have thousands of diagnostic type check block tests
that would greatly benefit if the general emit structure would still
match conceptually. This is another bonus argument on why changing the
way inputs are applied is probably an option we should consider as a
last resort.
Ultimately, there is a good solution where we unwrap directive signal
inputs, based on metadata, and access a brand type field on the
`InputSignal`. This ensures auto-completion continues to work as is, and
also the structure of type check blocks doesn't change conceptually. In
future commits we also need to handle type-inference for generic signal
inputs.
Note: Another alternative considered, in terms of using metadata or not.
We could have type helpers to unwrap signal inputs using type helpers
like: `T extends InputSignal<any, WriteT> ? WriteT : T`. This would
allow us to drop the input signal metadata dependency, but in reality,
this has a few issues:
- users might have `@Input`'s passing around `InputSignal`'s. This is
unlikely, but shows that the solution would not be fully correct.
- we need the metadata regardless, as we plan on accessing it at runtime
as well, to distinguish between signal inputs and normal inputs when
applying new values. This was not clear when this option was
considered initially.
PR Close#53521
This commit introduces a function for declaring inputs in
components. The function is called `input`. It comes in two flavors:
- `input` for optional inputs with initial values
- `input.required` for required inputs
Inputs are declared as class members, like with `@Input`- except that
the class field will no longer hold the input value directly. Angular
takes control over the input field and exposes the input value as a
signal. The runtime implementation will follow in future commits.
This commit simply introduces:
- initial compiler detection to recognize such inputs in classes
- the initial signature of `input` and `input.required`.
Note: the defer size test is flawed and there is no minification- hence
this commit also needs to incorporate the new dependency graph changes.
PR Close#53521
Joey Perrott