Thumbs

Thumbs of images are created automatically.
To create a thumb of a different source or overwrite the default thumb's image (for example, with an equivalent image of smaller resolution for increased performance), pass the URL or path of the image intended to be the thumb to the "data-thumb" attribute.

<a
    data-fslightbox="gallery"
    data-thumb="/Images/Thumbs/1.jpg"
    href="https://www.youtube.com/watch?v=3nQNiWdeH2Q"
>
	A YouTube video.
</a>

Or using the JavaScript "thumbs" array prop:

fsLightboxInstances["gallery"].props.thumbs = ["/Images/Thumbs/1.jpg"];

var svg = document.createElementNS("http://www.w3.org/2000/svg", "svg");
svg.setAttributeNS(null, "width", "30px");
svg.setAttributeNS(null, "height", "30px");
svg.setAttributeNS(null, "viewBox", "0 0 512 512");
var path = document.createElementNS("http://www.w3.org/2000/svg", "path");
path.setAttributeNS(null, "d","M490.24,113.92c-13.888-24.704-28.96-29.248-59.648-30.976C399.936,80.864,322.848,80,256.064,80c-66.912,0-144.032,0.864-174.656,2.912c-30.624,1.76-45.728,6.272-59.744,31.008C7.36,138.592,0,181.088,0,255.904C0,255.968,0,256,0,256c0,0.064,0,0.096,0,0.096v0.064c0,74.496,7.36,117.312,21.664,141.728c14.016,24.704,29.088,29.184,59.712,31.264C112.032,430.944,189.152,432,256.064,432c66.784,0,143.872-1.056,174.56-2.816c30.688-2.08,45.76-6.56,59.648-31.264C504.704,373.504,512,330.688,512,256.192c0,0,0-0.096,0-0.16c0,0,0-0.064,0-0.096C512,181.088,504.704,138.592,490.24,113.92z M192,352V160l160,96L192,352z");
svg.appendChild(path);
fsLightboxInstances["gallery"].props.thumbsIcons = [svg];

fsLightbox.props.showThumbsOnMount = true;

fsLightbox.props.disableThumbs = true;