How to code regex and function to output srcset

Hi, I’d like to ask you how to optimize the below code (both regex and function). It should check whether “img.file”, “img[x2]” and “img[x3]” exist and then return appropriate srcset. PS the script is written for Handlebars but it’s almost pure js. Regex should return only last part of the digits (example: 1.biwbvib55-3124-444.jpg => 444)


injectSrcSet: (img) => {
            // const regex = /\b(?:\d+)/g;
            const regex = /\b[^-](?:\d+)\b/g;

            let small, med, big, result;
            img.file ? small = `/images/${img.file}` + " " + `${img.file.match(regex)}` + "w" : null;
            img["2x"] ? med = `/images/${img["2x"]}` + " " + `${img["2x"].match(regex)}` + "w" : null;
            img["3x"] ? big = `/images/${img["3x"]}` + " " + `${img["3x"].match(regex)}` + "w" : null;
            if (small) {
                result = small
            } if (med) {
                result = result + ", " + med
            } if (big) {
                result = result + ", " + big
            }
            return `scrset="${result}"`
        },