reorders amazon search results to sort by price per weight to find the actually cheapest item (only tested on amazon.de)

amazon-sort-by-price-per-unit.js

// reorders amazon search results to sort by price per weight to find the actually cheapest item
// 1. install https://addons.mozilla.org/en-US/firefox/addon/weautopagerize/
// 2. search for something
// 3. scroll down all the way
// 4. run this script

// "featured by amazon"
for (let crap of document.getElementsByClassName(
    "template=FEATURED_ASINS_LIST"
))
    crap.remove();

function isHidden(el) {
    return el.offsetParent === null;
}

selectorItem = ".s-asin .sg-col-inner";
selectorPPU = ".a-text-normal .a-size-base.a-color-secondary";

getcur = () => $$(selectorItem).filter((x) => !isHidden(x));

tonum = ({ num, unit }) => {
    const unitmap = {
        kg: 1,
        "100g": 0.1,
        "100 g": 0.1,
        g: 0.001,
        gramm: 0.001,
        stück: 0.001, // fake
        unit: 0.001,
        beutel: 0.001,
    };
    const div = unitmap[unit.toLowerCase()];
    if (!div) throw Error(`unknown unit: ${unit}`);
    const res = +num.replace(".", "").replace(",", ".") / div;
    if (isNaN(res)) throw Error(`nan: ${num}/${unit}`);
    return res;
};
sorted = $$(selectorItem)
    .filter((x) => !isHidden(x))
    .map((ele) => {
        const ppu = ele.querySelector(selectorPPU);
        return {
            ele,
            txt: ppu?.textContent,
            val: ppu
                ? tonum(
                      /\((?<num>[\d.]+,\d+)\s+€\/(?<unit>.*)\)/.exec(
                          ppu.textContent
                      ).groups
                  )
                : 9999999,
        };
    })
    .sort((a, b) => a.val - b.val);

function swapElements(obj1, obj2) {
    // create marker element and insert it where obj1 is
    var temp = document.createElement("div");
    obj1.parentNode.insertBefore(temp, obj1);

    // move obj1 to right before obj2
    obj2.parentNode.insertBefore(obj1, obj2);

    // move obj2 to right before where obj1 used to be
    temp.parentNode.insertBefore(obj2, temp);

    // remove temporary marker node
    temp.parentNode.removeChild(temp);
}

(async () => {
    for (var i = 0; i < sorted.length; i++) {
        if (i % 10 === 0) console.log(`${i}/${sorted.length}`);
        // await new Promise(r => setImmediate(r));
        var curlist = getcur();
        swapElements(curlist[i], sorted[i].ele);
    }
    console.log("done!");
})();