pri.scaleblocks

It doesn't need to call somewhere. Loads when document ready. If you have to control it anyway, use window.disableAutoScaleBlocks property.

Simple usage in html

<div class="jzoom-item" data-scale-if="window.width < 640">
  <img width="640" height="480" src="http://shopbot.business/wp-content/uploads/Google-Pixel-4.jpg">
</div>