Advanced Configuration

The Script can be configured by adding specific parameters to the Script URL. Each of these parameters has a default that should be perfectly suited to your needs pretty much all the time.


Default value: 0.2 (any value that is not a number will be ignored)

The Script will lazy-load media by default. To avoid too abrupt a transition with elements appearing into view and then media very obviously loading afterwards, the Script will "anticipate" lazy loading by a factor of the actual viewport. This behaviour is controlled by anticipation.

With the default of 0.2 and for a viewport 800 pixels wide per 600 pixels high, the Script will consider as visible any element within a rectangle going from coordinates (-160,-120) to coordinates (960,720). You could set anticipation to 1 and anticipate lazy loading by an entire screen: the rectangle where elements are considered visible would then go from (-800,-600) to (1600,1200).

<!-- anticipate lazy-loading by half a screen -->
<script async defer src=""></script>

<!-- anticipate lazy-loading by an entire screen -->
<script async defer src=""></script>


Default value: "twic"

In the rare occurrence where twic is already in use on your page and you wish to avoid any potential collision, you can use this script parameter to change twic into something else entirely.

Note that every occurrence of twic must be replaced with whatever name you set this script parameter to.

So, the following configuration:

<script async defer src=""></script>

implies that:

  • attributes names are changed:
    • data-twic-background becomes data-batman-background
    • data-twic-background-* attributes become data-batman-background-*
    • data-twic-bot becomes data-batman-bot
    • data-twic-focus becomes data-batman-focus
    • data-twic-poster becomes data-batman-poster
    • data-twic-poster-* attributes become data-batman-poster-*
    • data-twic-src becomes data-batman-src
    • data-twic-src-* attributes become data-batman-src-*
    • data-twic-step becomes data-batman-step
    • data-twic-transform becomes data-batman-transform
  • views should be marked with data-batman-view rather than data-twic-view
  • life cycle class names are changed:
    • twic-loading becomes batman-loading
    • twic-done becomes batman-done
    • twic-error becomes batman-error
    • twic-poster-loading becomes batman-poster-loading
    • twic-poster-done becomes batman-poster-done
    • twic-poster-error becomes batman-poster-error
    • twic-background-loading becomes batman-background-loading
    • twic-background-done becomes batman-background-done
    • twic-background-error becomes batman-background-error


Default value: 2 (any value that is not a number will be ignored)

The Script will take the Device Pixel Ratio of the current device into consideration when determining the sizes of media to load. While this is the best approach in theory, it may clutter the bandwidth of portable devices with a high DPR but a fairly small screen surface relatively.

By default, the Script will not take a DPR greater than 2 into consideration. If the DPR of the device is higher than 2, the Script will assume it to be 2.

To alter this behaviour, change the value of max-dpr:

  • you can lower it (for instance by setting it to 1, effectively ignoring the DPR altogether)
  • or you can be more permissive (for instance by setting it to 3 or 4)
<!-- ignore DPR -->
<script async defer src=""></script>

<!-- handle DPR up to 4 -->
<script async defer src=""></script>


Default value: ""

The Script will prepend all your TwicPics image paths with the string provided through path. This is especially useful to easily switch from one environment to another (like between a staging and a production environment).

Let us take the following domain configuration as an example:

pathsource images URL
<!-- targets -->
<script async defer src=""></script>

<!-- targets -->
<script async defer src=""></script>

The following image element:

<img data-twic-src="image:asset.jpg">

will target

  • if path is set to staging
  • if path is set to prod
The value of path is added "as-is", so you have to be extra-careful with slashes and how you handle them. If all your image: URLs start with a slash, like image:/asset.jpg then path should not end with one. If, however, you do not have a leading slash in your image: URLs, as in image:asset.jpg , then path should end with a slash.


Default value: 10 (any value that is not a number will be ignored)

To avoid requesting too may variants of the same medium (as could happen in the case of width: 100% elements for instance), the Script will round the width of media to the closest multiple of step. The height will then be computed so as to respect the original aspect ratio.

For instance, with the default of 10, if the Script is told by CSS the size of an element is 334x146, it will round it down to 330x144. Alternatively, for an element that is 336x222, it will round the size up to 340x225.

You can change this value to get as close or as far from a pixel-perfect resizing as desired:

  • lowering it to 5 would potentially double the number of variants requested,
  • lowering it to 1 would be pixel-perfect all the time,
  • adjusting it up to 1000 would greatly reduce the number of variants but would stress the scaling algorithms of browsers more.

Note that the stepping value can still be overridden on a per-element basis using the data-twic-step attribute.

<!-- Pixel perfect -->
<script async defer src=""></script>

<!-- Less variants -->
<script async defer src=""></script>
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