perezoso.js (v1.1.0)

Perezoso is a lightweight javascript plugin to lazy load responsive images forked from fhopeman/justlazy.

Most of the existing javascript plugins using extensive dependencies or supporting just the img-tag without responsive parts. This plugin is supposed to be an alternative.

Features

• 100% performance with plain javascript (no jQuery).
• Simplicity and lightness (just lazy loading of images, no special cases).
• Heavily tested on various devices, browsers and OS versions.

Installation

File include

You can download the latest release and include the perezoso.js file as follows in your page:

<script src="javascript/perezoso.js" type="text/javascript"></script>

NPM

$ npm install perezoso

Documentation

1. Define attributes

Anything passed to the placeholder as data-* will became an attribute with the same name in the newly generated img.

Example:

<span data-src="path-to-image/image.jpg"
      data-alt="some alt text"
      data-srcset="path-to-image/image-600.jpg 600w, path-to-image/image-1000.jpg 1000w"
      data-title="some title"
      data-class="img-class"
      class="lazyload-placeholder">
</span>

Will became <img src="path-to-image/image.jpg" class="img-class" alt="some alt text" srcset="path-to-image/image-600.jpg 600w, path-to-image/image-1000.jpg 1000w" title="some title">.

2. Register event

There are three possiblities to trigger the lazy loading of the image(s).

The most comfortable one registers an event listener for all placeholders with a specific css class (e.g. lazyload-placeholder). The images will be loaded automatically if they become visible. The parameters are the css-class as string and optional options.

Perezoso.registerLazyLoadByClass(css-class[, options]);

If you need more flexibility, the next function accepts as first parameter the html object of the placeholder. So you can decide how to extract the placeholder objects out of the html. The parameters are the placeholder as object and options if you need them.

Perezoso.registerLazyLoad(placeholder[, options]);

Parameters

css-class

The css-class is a string which has to be provided without the class selector dot as prefix.

Example:

Perezoso.registerLazyLoadByClass('load-if-visible');

placeholder

The placeholder has to be provided as plain javascript object.

Example:

Perezoso.registerLazyLoad(document.getElementById('placeholder-1'));

threshold

The threshold option is optional. The image is loaded the defined pixels before it appears on the screen.

Example:

Perezoso.registerLazyLoadByClass('load-if-visible', {
    threshold: 200
});

onLoadCallback

The onLoadCallback option is optional. When the new image is created and loaded, the function defined here is called.

Example:

Perezoso.registerLazyLoadByClass('load-if-visible', {
    onLoadCallback: function() {
        console.log('image loaded!');
    }
});