A Tampermonkey script that converts currencies and whatnot on Amazon sites. WIP.

Global Amazon Script.js

// ==UserScript==
// @name         New Userscript
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  try to take over the world!
// @author       You
// @match        https://*.amazon.de/*
// @match        https://*.amazon.co.jp/*
// @match        https://*.amazon.co.uk/*
// @match        https://*.amazon.it/*
// @grant        none
// ==/UserScript==



function convertUnit(value, unit) {
    let multiplier = null;
    let dest = null;

    switch(unit.toLowerCase()){
        case 'kg':
        case 'kilograms':
            multiplier = 2.20462;
            dest = 'lbs';
            break;

        case 'g':
            multiplier = 0.220462;
            dest = 'lbs';
            break;

        case 'cm':
            multiplier = 0.393701;
            dest = 'in';
            break;

        case 'mm':
            multiplier = 0.0393701;
            dest = 'in';
            break;

        case '€':
            multiplier = 1.19;
            dest = '$';
            break;

        case '¥':
            multiplier = 0.14;
            dest = '$';
            break;

        case '$':
            multiplier = 1;
            dest = '$';
            break;


        default:
            alert(unit);
            break;
    }


    if(multiplier == null) { return {value: 'wtf', unit: 'wtf' }; }

    if(value instanceof Array) {
        value = value.map(v => v * multiplier);
    } else {
        value = value * multiplier;
    }

    return {value: value, unit: dest};
}

function convertValueStr(str, unit) {
    var input;
    if(str instanceof Array) {
        input = str.map(e => new Number(e.replace(',', '')));
    } else {
        input = new Number(str.replace(',', ''));
    }

    let result = convertUnit(input, unit);

    var format;

    var appendUnit = true;

    if(result.unit == '$') {
        appendUnit = false;
        let formatter = new Intl.NumberFormat('en-US', {
            style: 'currency',
            currency: 'USD',
        });
        format = v => formatter.format(v);
    } else {
        format = v => v.toFixed(2);
    }

    if(result.value instanceof Array) {
        let oldFormat = format;
        format = v => v.map(e => oldFormat(e)).join(' x ')
    }

    if(appendUnit) {
        return format(result.value) + ' ' + result.unit;
    } else {
        return format(result.value);
    }
}

function queryXpathRoot(root, path) {
    //"//*[@id='prodDetails']//span[@class='value']"
    return [document.evaluate(path, root, null, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null)].map(e => Array(e.snapshotLength).fill().map((a, i) => e.snapshotItem(i)))[0]
}


function iterXpathRoot(root, path, cb) {
    let elems = queryXpathRoot(root, path);
    for(const elem of elems) {
        cb(elem);
    }
}

function iterXpath(path, cb) {
    return iterXpathRoot(document, path, cb);
}

function indiscriminateValue(text) {
    const numreg = /(\d\d?\d?(?:,?\d\d\d)*(?:\.\d+)?)/g

    var found = false;
    text = text.replace(/(?:\b|^)([\d,]+(?:\.\d+)?)\s*x\s*(\d+(?:\.\d+)?)\s*x\s*(\d+(?:\.\d+)?)\s*(mm|cm)(?:\b|$)/g, (matched, p1Value, p2Value, p3Value, p4Unit) => {
        found = true;
        return convertValueStr([p1Value, p2Value, p3Value], p4Unit);

    });

    text = text.replace(/(?:\b|^)([€¥])\s*(\d\d?\d?(?:,?\d\d\d)*(?:\.\d+)?)(?:\b|$)/g, (matched, p1Unit, p2Value) => {
        found = true;
        return convertValueStr(p2Value, p1Unit);

    });

    text = text.replace(/(?:\b|^)(\d\d?\d?(?:,?\d\d\d)*(?:\.\d+)?)\s*(mm|cm|g|[Kk](?:ilo)?[Gg](?:rams)?)(?:\b|$)/g, (matched, p1Value, p2Unit) => {
        found = true;
        return convertValueStr(p1Value, p2Unit);

    });

    text = text.replace(/(?:\b|^)(\d\d?\d?(?:,?\d\d\d)*(?:\.\d+)?)\s*x\s*(\d\d?\d?(?:,?\d\d\d)*(?:\.\d+)?)\s*x\s*(\d\d?\d?(?:,?\d\d\d)*(?:\.\d+)?)\s*(mm|cm)(?:\b|$)/g, (matched, p1Value, p2Value, p3Value, p4Unit) => {
        found = true;
        return convertValueStr([p1Value, p2Value, p3Value], p4Unit);

    });

    return text;
}

function indiscriminate() {
    let list = [
        "//*[@id='prodDetails']//*[@class='value']",
        "//*[@id='prodDetails']//td",
        "//*[starts-with(@class, 'comparison_baseitem_column')]/span",
        "//*[starts-with(@class, 'comparison_sim_items_column')]/span",
        "//span[contains(@class, 'a-color-price')]",
        "//*[@id='price-shipping-message']/*[starts-with(text(), '+')]",
        "//*[@id='price_inside_buybox' or @id='priceblock_ourprice']",
        "//*[@id='price-shipping-message']/*[starts-with(text(), '+')]",
        "//span[contains(text(), ' delivery')]"

        ];
    let xpath = list.join(" | ")
    iterXpath(xpath, e => {
        let oldText = e.innerText;
        let newText = indiscriminateValue(e.innerText);
        if(oldText != newText) {
            e.innerText = indiscriminateValue(e.innerText);
        }
    });

    iterXpath("//*[@class='a-price']", e => {
        let unitNode = e.getElementsByClassName('a-price-symbol')[0];
        let valueNode = e.getElementsByClassName('a-price-whole')[0];
        if(unitNode.innerText == '') {
            let newText =  indiscriminateValue(valueNode.innerText);
            if(newText != valueNode.innerText) {
                valueNode.innerText = newText;
            }
        } else {
            let result = convertUnit(new Number(valueNode.innerText), unitNode.innerText);
            if(unitNode.innerText != result.unit) {
                unitNode.innerText = result.unit;
                valueNode.innerText = result.value.toFixed(2);
            }
        }
    });
}

function debounce(func, wait, immediate) {
    var timeout;
    return function() {
        var context = this, args = arguments;
        var later = function() {
            timeout = null;
            if (!immediate) func.apply(context, args);
        };
        var callNow = immediate && !timeout;
        clearTimeout(timeout);
        timeout = setTimeout(later, wait);
        if (callNow) func.apply(context, args);
    };
};

(function() {
    'use strict';
    var timerId;
    var debounceFunction  =  function (func, delay) {
	// Cancels the setTimeout method execution
	clearTimeout(timerId);

	// Executes the func after delay time.
	timerId  =  setTimeout(indiscriminate, delay);
};

    var mutated = debounce(indiscriminate, 100);

    new MutationObserver(function(mutations) {
        debounceFunction(300);
}).observe(document, {childList: true, subtree: true});


})();