react-scroll-activator

react-scroll-activator watches for a scroll event inside of a container or on the window. When certain user-defined rules are met, it passes an activatedState prop to a render prop component, triggering whatever behavior the developer chooses on the child.

The Problem

You want an element to "stick" to the top of the window when a user scrolls in a page. Or maybe you want to hide an element as a user scrolls. Basically, you want to trigger the behavior of a component as a user scrolls.

The Solution

react-scroll-activator is a straightforward React component that watches for a scroll event inside any container or on the window. If a user scrolls, (and a series of conditions are met), the ScrollActivator component sends an activatedState prop to a render prop component, triggering the render prop component's behavior.

Installation

npm install react-scroll-activator

Usage

• Basic

You can either use the ScrollActivator component on the window, or on any container that scrolls.

On the window

class StickyElement extends React.Component {
  shouldComponentBeSticky = () => {
    return window.scrollY > 120
  }

  isSticky = activatedState => {
    if (activatedState === 'isActivated') {
      return { position: 'fixed' }
    } else {
      return { position: 'relative' }
    }
  }

  render () {
    return (
      <ScrollActivator onScroll={this.shouldComponentBeSticky}>
        {activatedState => (
          <div style={this.isSticky(activatedState)}>
            <h1>Hi</h1>
          </div>
        )}
      </ScrollActivator>
    }
  )
}

In a modal

Let's say the modal's classname is .any-class-name:

class StickyElement extends React.Component {
  handleScrollCallback = (e, topOffset) => {
    this.containerSelector = document.querySelector('.any-class-name')
    return (
      e.target.scrollTop >
        this.containerSelector.getBoundingClientRect().top + topOffset
    )
  }

  render () {
    return (
      <div className='any-class-name'>
        <ScrollActivator
          onScroll={this.handleScrollCallback}
          containerSelector='.any-class-name'
        >
          {activatedState => <StickyElement isSticky={activatedState} />}
        </ScrollActivator>
      </div>
    )
  }
}

In this example, ScrollActivator is wrapped around a StickyElement which is the component that will stick to the top of the container as the user scrolls. The ScrollActivator will pass activatedState to the child component, which the child component can then use to activate certain behavior. In the case of this example, the StickyElement will stick to the top of the component.

To actually make sure you are setting rules, add a handleScrollCallback function that resembles the one below to the class in which you are invoking ScrollActivator. You'll pass this to the ScrollActivator component onScroll.

FAQ

Inspiration

I built this because I needed to make a banner stick to the top of a container, but I didn't have access to the window.

Alternatives

Contributors

Mae Capozzi

License

MIT

License

maecapozzi/react-scroll-activator

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