Conditional Visibility in Angular Templates

In Angular, conditional visibility is a common requirement where elements are shown or hidden based on certain conditions. This can be achieved using various directives and techniques.

Using the hidden Property

One way to conditionally show or hide an element is by binding to the hidden property. The [hidden] attribute can be used in conjunction with a boolean expression to determine whether an element should be visible or not.

<div [hidden]="!myVar">Content</div>

In this example, the div element will be hidden when myVar is false and shown when it’s true.

However, using the hidden property can lead to conflicts with CSS styles that set the display property. To avoid such issues, you can add a global style to your application:

[hidden] {
  display: none !important;
}

This ensures that elements with the [hidden] attribute will be properly hidden, even if they have conflicting CSS styles.

Using the *ngIf Directive

Another way to conditionally show or hide an element is by using the *ngIf directive. This directive removes the element from the DOM when the condition is false and adds it back when the condition becomes true.

<div *ngIf="myVar">Content</div>

In this example, the div element will be removed from the DOM when myVar is false and added back when it’s true.

Choosing Between [hidden] and *ngIf

Both [hidden] and *ngIf can be used to achieve conditional visibility, but they have different implications:

• [hidden] modifies the display property of an element, making it invisible while keeping it in the DOM.
• *ngIf removes the element from the DOM when the condition is false, which can improve performance by reducing the number of elements in the DOM.

When to use each approach:

• Use [hidden] when you need to toggle visibility frequently or when you want to keep the element in the DOM for accessibility or other reasons.
• Use *ngIf when you need to completely remove an element from the DOM, such as when working with complex components or large datasets.

Alternative Approaches

There are also alternative approaches to achieving conditional visibility:

• Using the [style.display] property:

“`
* Using a class binding:
“`html

“`
And then defining the `.hidden` class in your CSS:
“`css
.hidden {
display: none;
}
“`

Best Practices

When working with conditional visibility, keep the following best practices in mind:

• Use [hidden] or *ngIf instead of binding to the style.display property directly.
• Avoid using inline styles and prefer external CSS files for better maintainability.
• Consider accessibility implications when hiding elements, such as ensuring that screen readers can still access the content.

By following these guidelines and techniques, you can effectively manage conditional visibility in your Angular applications and create more dynamic and user-friendly interfaces.