Roller

Roller is a JavaScript class for rolling on a web page.

• Plain JavaScript - this class hasn't dependencies on external libraries, just plain JS;
• IE9+ supports - It works on IE9 and above;
• Behavioral pattern - It use this pattern, so you don't need to pass DOM-elements to the constructor;
• Recalculates after resizing supports - It can recalculates coordinates after window resizing.

Note this class only emits event (the default name is "rolling") type CustomEvent on element (the default element is document). The event object contains a reference to the element that is currently active. For more details see [the example] (./example/index.html) and settings.

Usage

Add the script to a page, initialize the class and attach a handler to the event "rolling". For example:

<script src="../dist/roller.min.js"></script>
<script>
  document.addEventListener("DOMContentLoaded", function() {
    var roller = new Roller();

    document.addEventListener("rolling", handler);

    roller.init();

    function handler(event) {
      var link      = event.detail.link;
      var className = "active";

      resetClass(className);
      if (link) {
        link.classList.add(className);
      }
    }

    function resetClass(className) {
      var links = document.querySelectorAll("a");

      Array.prototype.forEach.call(links, function(link) {
        link.classList.remove(className);
      });
    }
  });
</script>

Note method "init" calculates coordinates of the "rolling" areas. For more details see [below] (#loading).

You need to associate the link with the "rolling" area through attributes data-roller-area and data-roller-link:

<ul>
  <li><a href="#sec" data-roller-link="item1">list item</a></li>
</ul>
...
<section id="sec" data-roller-area="item1">section</section>

document will emits "rolling" event. You may change this emitted element via attribute data-roller-where:

<ul data-roller-where>
  <li><a href="#sec" data-roller-link="item1">list item</a></li>
</ul>
...
<section id="sec" data-roller-area="item1">section</section>

Now UL element will emit the event.

API and options

API:

• init() - Initialization method. For more details see [below] (#loading);
• resized - It has null before the initialization of the class. It has true If there was resizing window, else false.

Constructor options:

• attributeLink - string the attribute name for the link. Default: "data-roller-link";
• attributeArea - string the attribute name for the area. Default: "data-roller-area";
• attributeWhere - string the attribute name for the emitted element. Default: "data-roller-where";
• nameEvent - the name of emitted event. Default: "rolling".

Event:

• detail.name - the name of the current area. You specified this name into the attributtes "data-roller-area" and "data-roller-link";
• detail.link - the current link. This element has the attribute "data-roller-link";
• detail.area - the current area. This element has the attribute "data-roller-area".

Note these properties will be null If the current area isn't "rolling" area (hasn't attribute data-roller-area)! See example.

When I initialize the class?

If you have pictures that affect the height of the areas that at the time of the event DOMContentLoaded the pictures still won't load! You can use window.onload or similar function:

...
resourcesLoaded(document.querySelectorAll("img"), function() {
  roller.init();
});

function resourcesLoaded(resources, callback) {
  var loaded = 0;
  var count  = resources.length;

  Array.prototype.forEach.call(resources, function(item) {
    item.addEventListener("load", onload, false);
  });

  function onload(event) {
    if (++loaded === count) {
      callback();
    }
  }
};

Resized example

If you want the class recalculate the coordinates after each resizing window that you may attach handler on resize event:

...
var handlerResized = throttle(function() {
  roller.resized = true;
}, 500);

window.addEventListener("resize", handlerResized);

function throttle(doSomething, ms) {
  var running = false;

  return function() {
    if (running) {
      return;
    }

    var self = this;
    var args = arguments;

    if (window.requestAnimationFrame) {
      window.requestAnimationFrame(step);
    } else {
      step();
    }

    function step() {
      running = true;
      doSomething.apply(self, args);
      setTimeout(function() {
        running = false;
      }, ms);
    }
  };
};

Building

This class is built using webpack. You just need to run this command after cloning the repository from the cloned folder:

npm run build

License

MIT

Copyright © Selkin Vitaly, 2015