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‎src/app/angular/components/ng-essentials/ng-essentials.html‎

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@@ -26,15 +26,17 @@ <h2 class="note-heading">Custom Component (Standalone Project)</h2>
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<li>
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<strong>Import the required module</strong>
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<pre class="note-code"><code>import &#123; Component &#125; from '&#64;angular/core';</code></pre>
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<pre
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class="note-code"
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><code>import &#123; Component &#125; from '&#64;angular/core';</code></pre>
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</li>
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<li>
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<strong>Use the <code>&#64;Component</code> decorator</strong>
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<ul class="note-list">
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<li>
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This decorator provides metadata for the component, such as its
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selector, template, and styles.
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This decorator provides metadata for the component, such as its selector, template, and
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styles.
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</li>
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</ul>
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</li>
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<strong>Define a selector</strong>
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<ul class="note-list">
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<li>
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The selector tells Angular which elements on the screen should be
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controlled or replaced by our custom component.
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The selector tells Angular which elements on the screen should be controlled or replaced
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by our custom component.
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</li>
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<li>
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The convention is to use at least two words separated by a dash
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(Example: <code>app-header</code>).
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</li>
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<li>
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Using a single-word selector may conflict with built-in HTML
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elements.
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The convention is to use at least two words separated by a dash (Example:
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<code>app-header</code>).
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</li>
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<li>Using a single-word selector may conflict with built-in HTML elements.</li>
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</ul>
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</li>
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@@ -62,18 +61,226 @@ <h2 class="note-heading">Custom Component (Standalone Project)</h2>
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<ul class="note-list">
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<li>The template defines the HTML structure of the component.</li>
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<li>We can define it using:</li>
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<li>A string (inline template) where we write HTML directly.</li>
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<li>A separate file using <code>templateUrl</code>, where we provide the file path.</li>
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</ul>
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</li>
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<li>
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<strong>Set the standalone property</strong>
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<ul class="note-list">
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<li>Depending on the Angular version:</li>
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<li>Angular 19+: The standalone property is automatically set to true.</li>
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<li>Earlier versions: You must manually set standalone: true.</li>
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<li>For module-based components, set it to false.</li>
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</ul>
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</li>
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<li>
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<strong>Import the component into app.component.ts</strong>
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<ul class="note-list">
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<li>
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To use the HeaderComponent, import it in app.component.ts and include it in the
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template.
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</li>
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<pre class="note-code">
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<code>
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import &#123; Component &#125; from '&#64;angular/core';
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import &#123; HeaderComponent &#125; from './header.component';
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&#64;Component(&#123;
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selector: 'app-root',
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standalone: true,
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imports: [HeaderComponent],
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templateUrl: './app.component.html',
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styleUrls: ['./app.component.css']
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&#125;)
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</code>
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</pre>
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</ul>
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</li>
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<li>
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<strong>Some Angular Features</strong>
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<ul class="note-list">
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<li>
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A string (inline template) where we write HTML directly.
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Inside a component we can create variables and assign a value to it without using var,
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let and const keywords
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</li>
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<li>We a create regular variable outside the class and do regular javascript there</li>
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<pre class="note-code">
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<code>
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import &#123; Component &#125; from '&#64;angular/core';
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import &#123; DUMMY_USERS &#125; from '../../dummy-users';
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const randomIndex = Math.floor(Math.random() * DUMMY_USERS.length);
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&#64;Component(&#123;
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selector: 'app-user',
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standalone: true,
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templateUrl: './user.component.html',
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styleUrl: './user.component.css',
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&#125;)
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export class UserComponent &#123;
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selectedUser = DUMMY_USERS[randomIndex];
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&#125;
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</code>
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</pre>
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<li>We can also import a normal .ts file and use there values in our component</li>
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<pre class="note-code">
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<code>
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export const DUMMY_USERS = [
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&#123;
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id: 'u1',
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name: 'Jasmine Washington',
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avatar: 'user-1.jpg',
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&#125;,
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&#123;
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id: 'u2',
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name: 'Emily Thompson',
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avatar: 'user-2.jpg',
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&#125;,
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];
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</code>
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</pre>
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<li>
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A separate file using <code>templateUrl</code>, where we provide the
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file path.
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String interpolation – Display dynamic content. If we add
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<strong>private</strong> before the property, we can access it only inside the class. If
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we do not add <strong>public</strong>, it will be <strong>public by default</strong>. We
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can use other JavaScript expressions inside the interpolation <span>&#123;</span
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><span>&#123;</span> <span>&#125;</span><span>&#125;</span>
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</li>
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<pre class="note-code">
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<code>
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export class UserComponent &#123;
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private selectedUser = DUMMY_USERS[randomIndex];
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&#125;
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</code>
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</pre>
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<pre class="note-code">
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<code>
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&lt;p&gt;<span>&#123;</span><span>&#123;</span> selectedUser.name <span>&#125;</span><span>&#125;</span>&lt;/p&gt;
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</code>
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</pre>
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<li>
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Property Binding - Dynamic usage of html attribute. We can concatenate the src to get
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dynamic path
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</li>
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<pre class="note-code">
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<code>
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&lt;img [src]="<span>&#123;</span><span>&#123;</span> selectedUser.avatar <span>&#125;</span><span>&#125;</span>" alt="user-image" /&gt;
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</code>
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</pre>
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</ul>
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</li>
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<li>
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<strong>Set the standalone property</strong>
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<strong>Attribute Binding</strong>
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<ul class="note-list">
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<li>
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In Property Binding, Angular binds values to DOM properties, not attributes. For
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example:
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</li>
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<pre class="note-code">
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<code>
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&lt;img [src]="someSrc"&gt;
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</code>
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</pre>
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<li>Here, src is bound to the DOM property, not the HTML attribute.</li>
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<li>
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However, some attributes (like ARIA attributes) don’t have matching DOM properties. In
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such cases, Attribute Binding is used:
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</li>
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<pre class="note-code">
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<code>
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&lt;div
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role="progressbar"
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[attr.aria-valuenow]="currentVal"
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[attr.aria-valuemax]="maxVal"&gt;
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&lt;/div&gt;
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</code>
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</pre>
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<li>
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Adding attr. before an attribute tells Angular to bind the **HTML attribute instead of a
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property. This is useful for ARIA, colspan, tabindex, and other attributes without
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corresponding properties.
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</li>
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</ul>
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</li>
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<li>
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<strong>Typescript and Javascript features in classes [get]</strong>
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<ul class="note-list">
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<li>
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This is useful for dynamically displaying user profile images without hardcoding file
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paths.
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</li>
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<pre class="note-code">
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<code>
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get imagePath() &#123;
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return './assets/users/' + this.selectedUser.avatar;
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&#125;
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</code>
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</pre>
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<pre class="note-code">
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<code>
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&lt;div&gt;
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&lt;button&gt;
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&lt;img [src]="imagePath" [alt]="selectedUser.name" /&gt;
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&lt;span&gt;
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<span>&#123;</span><span>&#123;</span> selectedUser.name <span>&#125;</span><span>&#125;</span>
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&lt;/span&gt;
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&lt;/button&gt;
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&lt;/div&gt;
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</code>
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</pre>
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<li>Zone.js notifies Angular about user events, expired timers etc.</li>
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</ul>
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</li>
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<li>
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<strong>Signals</strong>
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<ul class="note-list">
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<li>
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A Signal is an object that stores a value (any type of value, including nested objects)
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There are two approaches for update state
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</li>
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<strong>Option 01:</strong>
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<li>Relying on Zone.js & Angular’s changes detection mechanism</li>
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<li>Works automatically, no special instruction mechanism</li>
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<li>Supports since Angular 2</li>
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<strong>Option 02:</strong>
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<li>Using Signals to notify angular about value changes & required Ui updates</li>
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<li>Requires usage & special “signal” instruction & code</li>
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<li>Supported since angular 16</li>
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<strong>How to use Signals</strong>
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<pre class="note-code">
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<code>
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import &#123; Component, signal &#125; from '&#64;angular/core';
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</code>
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</pre>
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<li>We need to call the signal to access the property inside it</li>
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<pre class="note-code">
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<code>
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selectedUser = signal(DUMMY_USERS[randomIndex]);
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imagePath = computed(() =&gt; './assets/users/' + this.selectedUser().avatar);
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get imagePath() &#123;
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return './assets/users/' + this.selectedUser().avatar;
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&#125;
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onSelectUser() &#123;
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const randomIndex = Math.floor(Math.random() * DUMMY_USERS.length);
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this.selectedUser = signal(DUMMY_USERS[randomIndex]);
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&#125;
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</code>
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</pre>
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</ul>
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</ol>
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</p>
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</div>
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</div>
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</section>
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</section>

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