ng-spy v4.0.2

ng-spy

A lightweight, dependecy-free scrollspy for angular. Use this library to spy on HTML elements on your page when the window is scrolled or resized.

This library provides directives and services to help you subscribe to new elements entering the browser window and possibly adds or remove CSS classes to these elements.

This library does not provide utilities to scrollTo spied elements and certainly does not handle link clicks. You have to handle these on your own.

Table of Contents

1. Example
2. Usage
3. Documentation
   • Directives
   • Services
   • Interfaces
   • Injection Tokens

Example

Checkout this example

Code for the previous example is also in this repository under the src folder.

Usage

1. npm install --save ng-spy

2. Import the module

   @NgModule({
     declarations: [],
     imports: [
       // ...
       ScrollSpyModule
     ],
     providers: [],
     bootstrap: [AppComponent]
   })
   export class AppModule { }

3. In your container component:

   ngAfterViewInit() {
     this.spyService.spy({ thresholdBottom: 50 });
   }

4. Use SpyTarget directive to mark element as a target:

   <h1 spyTarget="target-1">Hello, World!!</h1>

5. Optional: Use SpyOn directive to spy on a target:

   <a spyOn="target-1" activeClass="navbar__link--active" class="navbar__link" href="#target-1">target 1</a>

6. Alternatively, you can subscribe to activeSpyTarget from ScrollSpyService, which will emit every time a new element is active.

   this.scrollspyService.activeSpyTarget.subscribe(
     (activeTargetName: string) => console.log(activeTargetName)
   );

7. To start multiple spys you can scope the ScrollSpyService to a specific component or module in the providers array.

   // In component or module metadata:
   {
     // ...
     providers: [ ScrollSpyService ]
   }

Documentation

Directives

SpyOn

A directive to spy on a previously added target.

Input

SpyTarget

A directive to mark an element as a spy target.

Input

Services

ScrollSpyService

Functions

spy(spyOptions: SpyOptions): void

Starts spying on the targets. Call this on the top level container of your targets in AfterViewInit lifecycle hook. Without calling this function, nothing will happen.

Parameters:

addTarget(target: SpyTarget): void

adds the target to the targets collection for spying. This action will also trigger a check to re-evaluate the active target.

Parameters:

removeTarget(target: string): void

Removes a previously added target from the targets collection. This action will also trigger a check to re-evaluate the active target.

Parameters:

checkActiveElement(scrollContainer?: ElementRef): void

Tries to find the active target in the targets collection. If found it will emit the target name using the activeSpyTarget observable, Otherwise it will emit null.

Parameters:

isElementActive(element: ElementRef, scrollContainer?: ElementRef, currentActiveElement?: ElementRef): boolean

Checks if the element is inside the browser window and optionally inside the scrollContainer.

If a currentActiveElement is provided, it will also check if the element's offsetTop is greater than the currentActiveElement. Meaning, if two targets are active, only the last one on the screen will be emitted.

If a scrollContainer is provided, it will ignore thresholdBottom and thresholdTop in the window check and will instead check for the threshold inside the scrollContainer.

Parameters:

stopSpying(): void

Stops spying on the targets, completes the activeSpyTarget subject and clears the targets collection.

Getters

activeSpyTarget: Observable<string>

Use this to subscribe to new active spy targets. Value can be null if no target is found to be active.

Interfaces

SpyOptions

SpyTarget

InjectionTokens

RESIZE_TIME_THRESHOLD

Used in the resize event with auditTime.

Default Value: 300

SCROLL_TIME_THRESHOLD

Used in the scroll events with auditTime.

Default Value: 10