@defer
A type of block that can be used to defer load the JavaScript for components, directives and pipes used inside a component template.
Syntax
@defer ( on <trigger>; when <condition>; prefetch on <trigger>; prefetch when <condition> ) {
<!-- deferred template fragment -->
<calendar-cmp />
} @placeholder ( minimum? <duration> ) {
<!-- placeholder template fragment -->
<p>Placeholder</p>
} @loading ( minimum? <duration>; after? <duration> ) {
<!-- loading template fragment -->
<img alt="loading image" src="loading.gif" />
} @error {
<!-- error template fragment -->
<p>An loading error occured</p>
}
Description
Blocks
Supported sections of a defer block. Note: only the @defer block template fragment is deferred loaded. The remaining optional blocks are eagerly loaded.
| block | Description |
|---|---|
@defer |
The defer loaded block of content |
@placeholder |
Content shown prior to defer loading (Optional) |
@loading |
Content shown during defer loading (Optional) |
@error |
Content shown when defer loading errors occur (Optional) |
Triggers
Triggers provide conditions for when defer loading occurs. Some allow a template reference variable as an optional parameter. Separate multiple triggers with a semicolon.
| trigger | Triggers... |
|---|---|
on idle |
when the browser reports idle state (default) |
on viewport(<elementRef>?) |
when the element enters the viewport |
on interaction(<elementRef>?) |
when clicked, touched, or focused |
on hover(<elementRef>?) |
when element has been hovered |
on immediate |
when the page finishes rendering |
on timer(<duration>) |
after a specific timeout |
when <condition> |
on a custom condition |
Prefetch
Configures prefetching of the defer block used in the @defer parameters, but does not affect rendering. Rendering is handled by the standard on and when conditions. Separate multiple prefetch configurations with a semicolon.
@defer (prefetch on <trigger>; prefetch when <condition>) {
<!-- deferred template fragment -->
}
Learn more in the defer loading guide.