Scrollpoints

Scrollpoints lets you watch specific DOM-elements and fires a callback when an element enters or leaves the screen. It behaves similar to the jQuery Waypoints plugin, but does not depend on jQuery and is very small in size (~2KB).

Installation

Scrollpoints is available as npm module and bower component.

If you are using npm, call npm install scrollpoints --save to download the scrollpoints module and to add it to your package.json file. To use it with browserify, require it like this: var Scrollpoints = require('scrollpoints');

Using bower, simply install it with bower install scrollpoints and include the scrollpoints.js or scrollpoints.min.js file.

Documentation

Adding a new scrollpoint

To add a new scroll-handler function to a specific DOM-element, Scrollpoints provides the add function, which takes two arguments: the function to be executed and a configuration object.

First, we grab an element from the DOM.

var elem = document.querySelector('#my-awesome-element');

If the configuration object isn't provided to add, the default configuration will be used.

Scrollpoints.add(elem, function(domElement) {
    // this function will execute when elem entered the screen
});

If you want to customize behavior, add the config-object as the third parameter:

var config = {
    when: 'entering',
    reversed: true,
    once: false
};

Scrollpoints.add(elem, function(domElement) {
    /*
        This function will execute when elem starts to enter
        the screen (entering) from above, i.e. when the user
        scrolls upwards (reversed is set). It will happen
        every time the user scrolls past this point (once is set to false).
    */
}, config);

Scrollpoints follows the singleton design pattern. As such you may need to reinitialize the module. Use the destroy method before calling add again.

Scrollpoints.destroy().add(elem, function(domElement) {
    // ...
}, config);

Options

Options are per-element configurations to cause the plugin to behave differently. Add them as an object as third parameter to the add function.

when

Default value: 'entered'

Possible values:

• 'entered' Callback fires when the whole Element entered the screen.
• 'entering' Callback fires immediately when the element starts to enter the screen.
• 'leaving' Callback fires when the element starts to leave the screen.
• 'left' Callback fires when the element was scrolled off the screen completely

reversed

Default value: false

When set to true, upwards-scrolling is observed. For instance, when: 'entering' means when the user scrolls upwards and the element comes in from above, when: 'left' fires when an element has left the screen at the lower edge of the browser window, when scrolling back to top.

once

Default value: true

When a user scrolls to a specific element, the callback fires and is then disabled. Setting once to false, will cause the callback to execute every time when the user scrolls to the same point. If an entering callback is set, it will then execute when the user scrolls to that element, scrolling up and down to the element again will cause it to be called again.

offset

Default value: 0

Setting offset to, say, 200 on an entered scrollpoint, causes the callback to fire when the element entered the screen and the lower edge of the element has a 200px distance from the bottom of the browser window. Think of this property as "a specific amount of pixels too late". When an offset is set on a leaving element, it means that the callback will fire when the element is already x pixels out of the screen.

Overriding defaults

Scrollpoints provides a configure function to set the defaults for every new Scrollpoint.

Every Scrollpoint you create after this call will not only fire once, and will always fire 50px before the actual point.

Scrollpoints.configure({
    once: false,
    offset: -50
});