How does Angular show info on hover?

Angular primarily shows information on hover through the use of Tooltips, which are small, interactive pop-up messages. These components are designed to provide context-sensitive information or supplementary details when a user interacts with an element, most commonly by hovering their mouse pointer over it.

Understanding Angular Tooltips

A Tooltip component in the Angular ecosystem is a versatile pop-up that displays information or a message in response to user interaction. While "hover" is the most common trigger, tooltips can also be activated when users:

Hover over an element (e.g., an icon, button, or link).
Click on an interactive component.
Focus on an element using keyboard navigation.
Touch an element on touch-enabled devices.

These informational pop-ups can appear over various HTML elements, such as images, buttons, anchor tags (links), input fields, or custom components. The content displayed within a tooltip is highly flexible and can include:

Simple text messages.
Rich text formatting.
Images.
Hyperlinks.
Even complex custom templates with interactive elements.

Implementing Tooltips in Angular

While you can create custom tooltips using Angular directives and CSS, the most common and robust approach in professional Angular applications is to utilize a UI component library. Angular Material is the official and most popular choice for this, providing a comprehensive and accessible tooltip component.

1. Using Angular Material Tooltip

Angular Material offers a feature-rich tooltip component (MatTooltipModule) that is easy to integrate and highly customizable.

Installation and Setup

First, ensure you have Angular Material installed in your project:

ng add @angular/material

Then, import the MatTooltipModule into your Angular module (e.g., app.module.ts or a shared UI module):

import { MatTooltipModule } from '@angular/material/tooltip';

@NgModule({
  imports: [
    // ... other modules
    MatTooltipModule
  ],
  // ...
})
export class AppModule { }

Basic Usage

To add a tooltip to an HTML element, simply apply the matTooltip directive and assign the desired text message:

<button mat-raised-button
        matTooltip="Click to save your changes"
        matTooltipPosition="below"
        aria-label="Save button with tooltip">
  Save
</button>

In this example:

matTooltip: Contains the text message to display.
matTooltipPosition: Defines where the tooltip appears relative to the element (e.g., above, below, left, right, before, after).
aria-label: Essential for accessibility, describing the element's purpose for screen readers.

Key Customization Options

Angular Material's matTooltip directive provides several properties for fine-grained control:

Property	Type	Description	Default Value
`matTooltip`	`string`	The text content of the tooltip.
`matTooltipPosition`	`TooltipPosition`	Position relative to the element: `'above'`, `'below'`, `'left'`, `'right'`, `'before'`, `'after'`.	`'below'`
`matTooltipDisabled`	`boolean`	Whether the tooltip is disabled.	`false`
`matTooltipHideDelay`	`number`	Delay in milliseconds before the tooltip hides after the trigger leaves.	`0`
`matTooltipShowDelay`	`number`	Delay in milliseconds before the tooltip appears after the trigger enters.	`0`
`matTooltipClass`	`string \\| string[] \\| Set<string> \\| { [key: string]: any }`	Custom CSS class(es) to apply to the tooltip overlay.
`matTooltipEnterDelay`	`number`	Time in milliseconds to wait before showing the tooltip. Deprecated, use `matTooltipShowDelay`.	`0`
`matTooltipLeaveDelay`	`number`	Time in milliseconds to wait before hiding the tooltip. Deprecated, use `matTooltipHideDelay`.	`0`

Positioning: Control where the tooltip appears to avoid obscuring important content.
Delays: Set matTooltipShowDelay and matTooltipHideDelay to provide a smoother user experience, preventing tooltips from appearing and disappearing too quickly.
Disabling: Temporarily disable a tooltip using matTooltipDisabled.
Custom Styling: Use matTooltipClass to apply custom CSS for specific branding or visual requirements.

For more advanced scenarios, Angular Material also supports custom tooltip templates using matTooltip with ng-template, allowing you to embed rich HTML, images, and even other Angular components within the tooltip itself.

2. Custom Tooltip Directive (Advanced)

For highly specific requirements not met by existing libraries, developers can create a custom Angular directive to implement tooltip functionality. This typically involves:

Listening to Host Events: Using @HostListener to detect mouseenter and mouseleave events.
Dynamic Component Creation: Programmatically creating and attaching a tooltip component (e.g., using ComponentFactoryResolver and ViewContainerRef) to the DOM when mouseenter occurs.
Positioning Logic: Calculating the correct position for the tooltip relative to the host element.
Cleanup: Destroying the tooltip component on mouseleave.

While offering maximum flexibility, this approach requires more effort to manage styling, accessibility, and responsiveness compared to using a pre-built library.

Best Practices for Tooltips

To ensure tooltips enhance the user experience effectively:

Keep it Concise: Tooltips should provide supplementary, brief information, not full explanations.
Prioritize Accessibility: Always include aria-label for screen readers. Ensure tooltips are keyboard-navigable and accessible for users who cannot use a mouse. Angular Material's tooltips are built with accessibility in mind.
Avoid Overuse: Too many tooltips can be distracting and clutter the UI. Use them judiciously for non-obvious elements or actions.
Consistent Placement: Maintain a consistent position for tooltips across similar elements where possible.
Consider Delays: Implement slight showDelay and hideDelay to make their appearance and disappearance less jarring.

By leveraging the robust features of Angular Material's tooltip component, developers can effectively display contextual information on hover, significantly improving the usability and clarity of their Angular applications.