{"id":1994,"date":"2024-02-28T15:03:10","date_gmt":"2024-02-28T23:03:10","guid":{"rendered":"https:\/\/www.angulartraining.com\/daily-newsletter\/?p=1994"},"modified":"2024-02-28T15:03:10","modified_gmt":"2024-02-28T23:03:10","slug":"viewchild-and-contentchild-for-signal-based-queries","status":"publish","type":"post","link":"https:\/\/www.angulartraining.com\/daily-newsletter\/viewchild-and-contentchild-for-signal-based-queries\/","title":{"rendered":"viewChild() and contentChild() for signal-based queries"},"content":{"rendered":"\n

After introducing model()<\/code> for signal-based 2-way bindings<\/a>, let’s dive into viewChild()<\/a><\/code> and contentChild()<\/a><\/code> for signal-based queries.<\/p>\n\n\n\n

In case you’re not familiar with Angular queries, they existed before Angular 17.2 as the @ViewChild<\/a><\/code> and @ContentChild<\/a><\/code> decorators.<\/p>\n\n\n\n

ViewChild<\/strong> is a way to get a reference on an HTML within the current component’s template. For instance, if we need our Typescript to access the instance of a given child component, I can use @ViewChild<\/code> like so:<\/p>\n\n\n

\n
\"\"<\/figure>\n<\/div>\n\n\n

<\/p>\n\n\n\n

The new syntax gives us the same feature as a Signal:<\/p>\n\n\n

\n
\"\"<\/figure>\n<\/div>\n\n\n

<\/p>\n\n\n\n

The same goes with ContentChild<\/strong>. The difference between ViewChild <\/strong>and ContentChild<\/strong> is that ViewChild <\/strong>looks for an element inside the component’s template, whereas ContentChild<\/strong> looks for an element projected by the parent component into the ng-content<\/code> element of the current component using content projection. You can learn more about content projection with this tutorial<\/a>:<\/p>\n\n\n

\n
\"\"<\/figure>\n<\/div>\n\n\n

<\/p>\n\n\n\n

The above code will look for an element with a template reference variable<\/a> called test <\/strong>in the projected ng-content<\/code>.<\/p>\n\n\n\n

We can achieve the same feature with the new contentChild()<\/code> function, which returns a Signal:<\/p>\n\n\n

\n
\"\"<\/figure>\n<\/div>\n\n\n

<\/p>\n\n\n\n

Differences between these new functions and the old decorators<\/h3>\n\n\n\n

These new functions bring a few extra interesting features. For instance, we can get rid of possibly undefined<\/code> values by making a query required<\/code>:<\/p>\n\n\n\n

<\/p>\n\n\n

\n
\"\"<\/figure>\n<\/div>\n\n\n

<\/p>\n\n\n\n

Decorator-based queries were satisfied once the component was fully initialized, which means that running side effects required the use of specific lifecycle methods:<\/p>\n\n\n

\n
\"\"<\/figure>\n<\/div>\n\n\n

<\/p>\n\n\n\n

With signal-based queries, we receive a signal so we can rely on computed()<\/a><\/code> or effect()<\/a><\/code> to run such side-effects:<\/p>\n\n\n

\n
\"\"<\/figure>\n<\/div>\n\n\n

<\/p>\n\n\n\n

This approach is less intrusive and requires knowing just one thing: Signals! No more lifecycle methods are needed. You can find these different examples in action on Stackblitz here<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"

After introducing model() for signal-based 2-way bindings, let’s dive into viewChild() and contentChild() for signal-based queries. In case you’re not familiar with Angular queries, they existed before Angular 17.2 as the @ViewChild and @ContentChild decorators. ViewChild is a way to get a reference on an HTML within the current component’s template. For instance, if we […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4,29],"tags":[],"class_list":["post-1994","post","type-post","status-publish","format-standard","hentry","category-angular","category-signals"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.angulartraining.com\/daily-newsletter\/wp-json\/wp\/v2\/posts\/1994","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.angulartraining.com\/daily-newsletter\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.angulartraining.com\/daily-newsletter\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.angulartraining.com\/daily-newsletter\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.angulartraining.com\/daily-newsletter\/wp-json\/wp\/v2\/comments?post=1994"}],"version-history":[{"count":2,"href":"https:\/\/www.angulartraining.com\/daily-newsletter\/wp-json\/wp\/v2\/posts\/1994\/revisions"}],"predecessor-version":[{"id":2003,"href":"https:\/\/www.angulartraining.com\/daily-newsletter\/wp-json\/wp\/v2\/posts\/1994\/revisions\/2003"}],"wp:attachment":[{"href":"https:\/\/www.angulartraining.com\/daily-newsletter\/wp-json\/wp\/v2\/media?parent=1994"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.angulartraining.com\/daily-newsletter\/wp-json\/wp\/v2\/categories?post=1994"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.angulartraining.com\/daily-newsletter\/wp-json\/wp\/v2\/tags?post=1994"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}