Demonstrates one method of adding floating-point refined metal values in JavaScript.

addRefineds.js

// Source:
// https://github.com/Nicklason/node-tf2-currencies

const ONE_REF_SCRAP = 9;

// Convert a number in refined to scrap
function toScrap(refined) {
    return Math.round(refined * ONE_REF_SCRAP);
}

// Convert a number in scrap to refined
function toRefined(scrap) {
    if (scrap === 0) {
        // If the number is 0, no need to do any calculations
        return 0;
    }
    
    // Convert back into a number in refined
    scrap = scrap / ONE_REF_SCRAP;
    
    // Truncate to 2 decimal places
    return truncate(scrap, 2);
}

// Truncate a number to a certain number of decimal places
function truncate(number, places) {
    const pow = Math.pow(10, places);
    
    number = Math.abs(number * pow);
    
    const isPositive = number >= 0;
    // If we add 0.001 and it is greater than the number rounded up,
    // then we need to round up to fix floating point error
    const round = number + 0.001 > Math.ceil(number) ? Math.round : Math.floor;
    
    number = round(number);
    
    if (!isPositive) {
        number *= -1;
    }
    
    return number / pow;
}

function addRefineds(...currencies) {
    // Convert all currencies to scrap
    const scrap = currencies.reduce((total, currency) => total + toScrap(currency), 0);
    
    // Now back to refined
    return toRefined(scrap);
}

// Add 1.33 ref and 0.11 ref together
const metal = addRefineds(1.33, 0.11);

console.log(metal); // 1.44