Element.crossfade is a MooTools extension to simulate a tween for background-image element’s property.

The syntax, in this new version, is very clear:

document.id('el').crossfade('end_image.jpg');

Just remember your element position property in CSS should be expressly declared (as absolute, relative or fixed), don’t leave it blank.

Note: you can customize the fade behavior by setting tween properties

document.id('el').set('tween', {duration:5000});

These will be inherited by ‘crossfade’ animation.

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