A simple copy to clipboard button; is used at https://github.com/libgdx/libgdx.github.io

clipboard.js

/* Simple copy to clipboard action
 * ---
 * This script adds a simple "copy to clipboard" button to code elements located within <pre> elements. 
 * Requires jQuery. Can be used with the Jekyll Minimal Mistakes theme by adding it to the 'after_footer_scripts'.
 */
function sleep(ms) {
    return new Promise(resolve => setTimeout(resolve, ms));
}

async function onClickEffect(btn, style) {
    btn.removeClass("btn-light");
    btn.addClass(style);
    await sleep(250);
    btn.removeClass(style);
    btn.addClass("btn-light");
}

$(document).ready(function() {
    // Create butons
    $(".page__content pre > code").each(function() {
        $(this).parent().prepend(
            $(document.createElement('button')).prop({
                type: 'button',
                innerHTML: '<i class="far fa-copy"></i>',
            })
            .attr('title', 'Copy to clipboard')
            .addClass('btn')
            .addClass('btn--primary')
            .css('position', 'absolute')
            .css('right', '1em')
            // Click listener
            .on('click', function() {
                let codeElement = $(this).parent().children('code').first();

                if (!codeElement) {
                    throw new Error("Unexpected error! No corresponding code block was found for this button.");
                }

                // Blink effect
                onClickEffect($(this), "btn--success")

                // Copy to clipoard function
                navigator.clipboard.writeText($(codeElement).text()).then(() => true, () => true);
                return true;
            })
        );
    });
});