@ViewChild()¶

This decorator is inspired by Angular’s @ViewChild decorator and allows you to observe changes in the view child element of a Stencil component and set the value of a decorated property with the latest emitted value from the observable created by the viewChildObservable() operator.

Property may be decorated with @State() decorator to trigger re-render of the component when the value of the property changes.

It is alternative approach to JSX’s ref attribute.

Warning

Performances of this decorator will have same caveats as the used underlying observable. Read the documentation of the viewChildObservable() operator for more information about performance considerations.

ViewChild(selector, options)¶

Decorates a property with an observable emitting the view child element of a Stencil component that matches the given selector and sets the value of the decorated property with the latest emitted value from the observable created by the viewChildObservable() operator.

function ViewChild<E extends Element = Element>(selector: string, options?: ViewChildOptions): PropertyDecorator

Arguments:

selector (string) – The CSS selector to match the view child element.
options (ViewChildOptions) – Optional configuration for the decorator.

Returns:

Property decorator that sets the value of the decorated property with the latest emitted value from the observable created by the viewChildObservable() operator.

Return type:

PropertyDecorator

class ViewChildOptions()¶

Configuration options for observing a view child element.

export type ViewChildOptions = {
     cached?: boolean;
     filter?: ElementFilterFn | boolean;
     whileConnected?: boolean;
     distinct?: ElementComparatorFn | boolean;
};

ViewChildOptions.cached¶

Type:: boolean

Optional: Yes

Default: false

If true, property will be set only once, with the value of the view child element, if found. However, with filter option set, property will be set only once with the value of the filtered element.

ViewChildOptions.filter¶

Type:: ElementFilterFn | boolean

Optional: Yes

Default: false

Controls whether the property will be set only with the value of the filtered element. If true, the property will be set only when the view child element is found. If false, the property will be set with the value of the view child element, if found, or null if not found. If a function is provided, it will be used to filter the view child element and the property will be set only with the value of the filtered element.

ViewChildOptions.whileConnected¶

Type:: boolean

Optional: Yes

Default: false

If true, the property will be set only when the component is connected to the DOM. When component is disconnected, the property will not be set with any values. However, when component is re-connected, the property will be set with the current value, if it has changed in the meantime. You may use this option to avoid unnecessary recalculations or side effects when the component is not in the DOM, preserving last set value.

ViewChildOptions.distinct¶: Underlying implementation of the decorator uses viewChildObservable() operator. See the documentation of the operator for more information about this option.