Light weight library to observe the viewport scroll position.

In previous versions this package injected a scroll bar showing the scrolling progress. Why did I change it? Because it wasn't flexible to be adapted to others uses or UI libraries.

This means you still can create a progress bar as before and even with less code, keep scrolling to the Recipes section to see how.

Include the dist file in a script tag or run npm install scrollprogress --save.

In this last version, you have to create a new instance to create an observer and pass a callback to the contructor. That observer can be destroy at any time.

import ScrollProgress from 'scrollprogress';

const progressObserver = new ScrollProgress((x, y) => {
  console.log(x, y);
});

The callback will get two arguments, the first one being a decimal number for the horizontal scrolling progress and the second one for the vertical scrolling progress.

The method you pass will also get called on resize since the viewport and body metrics might change.

Whenever you want the observer to stop working just call progressObserver.destroy().

To accomplish the old functionality you will need to add the DOM element and the styles, something that the old version did for you, and then create an observer to update the bar width.

<div class="progress-bar"></div>

.progress-bar {
  background-color: rebeccapurple;
  height: 5px;
  position: fixed;
  top: 0;
  bottom: 0;
}

const progressElement = document.querySelector('.progress-bar');

const progressObserver = new ScrollProgress((x, y) => {
  progressElement.style.width = y * 100 + '%';
});

And that's it! Super simple.

Remember the only thing that the script will control will be the width of the progress bar as you scroll, the rest of the styling is all on you.

One of the main reasons this library was moved to this new approach is because you can easily couple an observer with any component library used nowadays. For example, create a React scroll bar component.

import { Component } from 'react';
import ScrollProgress from 'scrollprogress';

export default class ScrollProgress extends Component {
  constructor() {
    this.state = {
      progress: 0
    };
  }

  componentDidMount() {
    this.progressObserver = new ScrollProgress((x, y) => {
      this.setState({ progress: y * 100 });
    });
  }

  componentWillUnmount() {
    this.progressObserver.destroy();
  }

  render() {
    const style = {
      backgroundColor: 'rebeccapurple',
      height: '5px',
      position: 'fixed',
      top: 0,
      bottom: 0,
      width: `${this.state.progress}%`
    };

    return (
      <div
        className="progress-bar"
        style={ style }
      />
    );
  }
}

It's easy to imagine how to create the same component for other frameworks. If you want to add a recipe or any other use case to the documentation clone this repo and make a pull request.

The MIT License (MIT)

Copyright (c) 2017 Jeremias Menichelli

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
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SOFTWARE.