When the `NgIf` directive is used in a template, its context variables
can be used to capture the bound value. This is typically used together
with a pipe or function call, where the resulting value is captured in a
context variable. There's two syntax forms available:
1. Binding to `NgIfContext.ngIf` using the `as` syntax:
```html
<span *ngIf="(user$ | async) as user">{{user.name}}</span>
```
2. Binding to `NgIfContext.$implicit` using the `let` syntax:
```html
<span *ngIf="user$ | async; let user">{{user.name}}</span>
```
Because of the semantics of `ngIf`, it is known that the captured
context variable is non-nullable, however the template type checker
would not consider them as such and still report errors when
`strictNullTypes` is enabled.
This commit updates `NgIf`'s context guard to make the types of the
context variables non-nullable, avoiding the issue.
Fixes#34572
PR Close#35125
This is a follow-up to #33997 where some new generic parameters were added without defaults which is technically a breaking change. These changes add the defaults.
PR Close#34206
`<div class="hero-list" *ngIf="heroes else loading">` defines `heroes` as condition, but `hero-list` is used as condition in the transformed code `<ng-template [ngIf]="heroes" [ngIfElse]="loading">`.
PR Close#33425
A structural directive can specify a template guard for an input, such that
the type of that input's binding can be narrowed based on the guard's return
type. Previously, such template guards could only be methods, of which an
invocation would be inserted into the type-check block (TCB). For `NgIf`,
the template guard narrowed the type of its expression to be `NonNullable`
using the following declaration:
```typescript
export declare class NgIf {
static ngTemplateGuard_ngIf<E>(dir: NgIf, expr: E): expr is NonNullable<E>
}
```
This works fine for usages such as `*ngIf="person"` but starts to introduce
false-positives when e.g. an explicit non-null check like
`*ngIf="person !== null"` is used, as the method invocation in the TCB
would not have the desired effect of narrowing `person` to become
non-nullable:
```typescript
if (NgIf.ngTemplateGuard_ngIf(directive, ctx.person !== null)) {
// Usages of `ctx.person` within this block would
// not have been narrowed to be non-nullable.
}
```
This commit introduces a new strategy for template guards to allow for the
binding expression itself to be used as template guard in the TCB. Now,
the TCB generated for `*ngIf="person !== null"` would look as follows:
```typescript
if (ctx.person !== null) {
// This time `ctx.person` will successfully have
// been narrowed to be non-nullable.
}
```
This strategy can be activated by declaring the template guard as a
property declaration with `'binding'` as literal return type.
See #30235 for an example where this led to a false positive.
PR Close#30248
This commit adds an ngTemplateGuard_ngIf static method to the NgIf
directive and an ngTemplateContextGuard static method to NgFor. The
function of these two static methods is to enable type narrowing
within generated type checking code for consumers of the directives.
PR Close#26203
Allows a directive to use the expression passed directly to a property
as a guard instead of filtering the type through a type expression.
This more accurately matches the intent of the ngIf usage of its template
enabling better type inference.
Moved NgIf to using this type of guard instead of a function guard.
Closes: #20967
Structural directives can now specify a type guard that describes
what types can be inferred for an input expression inside the
directive's template.
NgIf was modified to declare an input guard on ngIf.
After this change, `fullTemplateTypeCheck` will infer that
usage of `ngIf` expression inside it's template is truthy.
For example, if a component has a property `person?: Person`
and a template of `<div *ngIf="person"> {{person.name}} </div>`
the compiler will no longer report that `person` might be null or
undefined.
The template compiler will generate code similar to,
```
if (NgIf.ngIfTypeGuard(instance.person)) {
instance.person.name
}
```
to validate the template's use of the interpolation expression.
Calling the type guard in this fashion allows TypeScript to infer
that `person` is non-null.
Fixes: #19756?
PR Close#20702
BREAKING CHANGE: the compiler option `enableLegacyTemplate` is now disabled by default as the `<template>` element has been deprecated since v4. Use `<ng-template>` instead. The option `enableLegacyTemplate` and the `<template>` element will both be removed in Angular v6.
PR Close#18756
Only one h1 is allowed per document, and this is provided by the template.
So we cannot have any h1 tags (or `#` markdown shorthand) in any API docs.
Closes#16193
* feat(common): support `as` syntax in template/* bindings
Closes#15020
Showing the new and the equivalent old syntax.
- `*ngIf="exp as var1”`
=> `*ngIf="exp; let var1 = ngIf”`
- `*ngFor="var item of itemsStream |async as items”`
=> `*ngFor="var item of itemsStream |async; let items = ngForOf”`
* feat(common): convert ngIf to use `*ngIf="exp as local“` syntax
* feat(common): convert ngForOf to use `*ngFor=“let i of exp as local“` syntax
* feat(common): expose NgForOfContext and NgIfContext
