Prefetch.js

var kryoPrefetch = {
    _init: function() {
        debug = true;
        store = {
            clicked: undefined,
            mouseDown: false,
            targetMatch: false,
            pending: false,
            href: ""
        };
        document.addEventListener("mousedown", e => {
            let target = e.target;
            let parent = target.parentElement;
            let child = target.querySelector("a");
            store.clicked = target;
            if (child !== null) {
                target = child;
            } else if (parent.tagName === "A") target = parent;
            if (target.tagName === "A") {
                store.href = target.href;
                store.mouseDown = true;
                let node = document.createElement('div');
                node.innerHTML = `<link rel=prefetch href="${target.href}" onload="kryoPrefetch.complete()" />`;
                document.querySelector('head').appendChild(node.childNodes[0]);
                store.pending = true;
                e.preventDefault();
            }
        });
        document.addEventListener("mouseup", e => {
            store.targetMatch = store.clicked === e.target;
            if (!store.pending) {
                if (store.targetMatch) {
                    window.location.href = store.href;
                    if (debug) console.log(store);
                }
            }
        });
        document.addEventListener("click", e => {
            if (store.mouseDown) e.preventDefault();
            store.mouseDown = false;
        });
        return store;
    }(),
    complete: function() {
        store.pending = false;
        if (!store.mouseDown) {
            if (store.targetMatch) {
                window.location.href = store.href;
                if (debug) console.log(store);
            }
        }
    }
}

prefetchWith$$.js

var kryoPrefetch = {
	_init: function() {
		$$("a")
		.on("mousedown",e=>{
			store.mouseDown = true;
			$$("head").append('<link rel=prefetch href="'+e.href+'" onload="kryoPrefetch.complete()" />');
			store.pending = true;
            e.preventDefault();
		})
		.on("mouseup",e=>{
			if (!store.pending) window.location.href = store.href;
		})
		.on("click",e=>{
			if (store.mouseDown) e.preventDefault();
            store.mouseDown = false;
		})
	}(),
	complete: function() {
        store.pending = false;
        if (!store.mouseDown) window.location.href = store.href;
    }
}