verlok

Real picture tag polyfill, to use responsive images today!

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Readme

picturePolyfill 4

Name: picturePolyfill
Brand: picturePolyfill
SKU: //verlok/picturepolyfill
Rating: 2.2425 (197 reviews)

A Responsive Images approach that you can use today that uses the real

picture

element along with children

source

elements with

media

src

and

srcset

attributes.

Author: Andrea Verlicchi (c) 2014
License: MIT/GPLv2

DEMO

picturePolyfill advantages

PicturePolyfill is fast and easy to use because:

markup & go: it uses the picture tag, easy to markup, and future-proof
loading performance: it serves only one image to your website users, no double HTTP requests are made
computing performance: it's designed and coded keeping performance in mind. For example:
- it doesn't execute repeatedly while a smooth/animated browser resize is in progress, avoiding useless DOM parsing and useless HTTP requests to mid-breakpoints images that the user might not need)
- it caches che
  source
  elements data, making the script much more performing see tests
support to HD (Retina) displays easily made via the
```
srcset
```
attribute of
```
source
```
tags
it's solid, because its code is all covered by tests

Differences with picturefill

picturePolyfill only polyfills the

picture

tag, whereas picturefill polyfills also the

img

tag with

srcset

sizes

attributes. Go for picturefill if you need to polyfill that too. If you don't, stick with picturePolyfill because it's a much smaller and faster script.

Markup pattern and explanation

With HD (Retina) images support

To support HD (Retina) images, mark up your responsive images like this.

Without HD (Retina) support

If you don't need to support HD (Retina) images, you can mark up your responsive images like this.

Notes about the markup

```
picture
```
tag:
- ```
data-default-src
```
  attribute: the image URL that you want to load in IE Desktop < 10.
- ```
data-alt
```
  attribute: the alternative text that will be set in the
```
img
```
  tag
```
source
```
tags:
- ```
media
```
  attribute: any media query, but it's advised to use a
```
min-width
```
  media query to follow the "mobile first" approach.
- ```
src
```
  attribute: the image URL at the corresponding
```
media
```
- ```
srcset
```
  attribute: comma separated URLs and scale at the corresponding
```
media
```
  , e.g.
```
img/768x768.gif, img/768x768x2.gif 2x
```
```
img
```
tag:
- one
```
img
```
  tag inside the
```
picture
```
  tag is required by the specs
- you can still use an empty
```
src
```
  in the
```
img
```
  to avoid a double http call in browsers that don't natively support the
```
picture
```
  tag.

NEW in version 4.0.0! The

source

tags order is important! The parser exits at first matching

media

so be sure to place the higher

min-width

queries at the begin of the tags list!

How the

img

is updated

The script searches in the

source

tags and selects the last matching

media

src

srcset

. When found, picturePolyfill will update the

img

element's

src

and

srcset

attributes inside the

picture

tag, with the matching ones. The

img

src

attribute is then updated at browser resize (see computing performance section above to read about performance at browser resize).

Server-side scaling/cropping tool

Responsive images can be quite complicated to be served on your website if you have to: pre-scale them at many different resolutions; name them; and maybe change their size when developing a new release of your site.

It's then a good practice to have a server-side picture scaling service (like pixtulate) to scale the images for you, just in time, starting from only one big image.

If you want to use an image server, you can code your HTML like the following:

Note that you should serve double resolution images (double width and double height) for HD/retina displays, as you can see in the "With HD (Retina) images support" section of this readme.

Take a look at the demo.

Installation

Manually

Download picturePolyfill from GitHub
Include the minified file in your project script directory

Using bower

You can install the latest version of picturePolyfill using bower

bower install picturePolyfill

Inclusion

You can either include the

script in the

head

section of your

HTML

pages, OR just before the closure of the

body

tag.

In the

head

section

    ...
    <script src="picturePolyfill.min.js" defer></script>


    ...

Note: Including the

defer

attribute in the

script

tag will prevent the script download to block page rendering while in progress.

At the end of the

body

section

    ...


    ...
    <script src="picturePolyfill.min.js"></script>

Execution

PicturePolyfill executes either automatically and by code, calling the parse() function.

it executes automatically at page load, on the whole
```
document
```
it executes automatically at browser resize, on the whole
```
document
```
it can be manually executed, if you:
- call
```
picturePolyfill.parse()
```
  to execute it on the whole
```
document
```
- call
```
picturePolyfill.parse(element)
```
  to execute from the
```
element
```
  DOM node below

After DOM has changed (AJAX calls, etc.)

PicturePolyfill is intentionally exposed to the global namespace, so you can call it as you need it.

Example: if some of your AJAX calls change a portion of your DOM injecting new

picture

nodes, after your new DOM has changed just call

picturePolyfill.parse()

(or

picturePolyfill.parse(element)

) to make picturePolyfill parse only the changed portion of the DOM.

Calling

picturePolyfill.parse(element)

(where

element

is a specific DOM node) is faster if you know the parent node where the DOM changed.

Browser support

PicturePolyfill supports all modern browsers and down to Internet Explorer 7.

On Modern Browsers, Internet Explorer 10 and above: the images will be loaded depending on the matched media query
On Internet Explorer 7 to 9: the content of the
```
data-default-src
```
attribute will be used to reference the image source.

Size and delivery

Currently,

picturePolyfill.js

compresses to around 1300bytes (~1.2kb) after minify and gzip. To minify, you might try these online tools: Uglify, Yahoo Compressor, or Closure Compiler. Serve with gzip compression.