public/search.js

'use strict';
/**
 * @param {string} input
 * @param {string} template Template for a search query.
 * @returns {string} Fully qualified URL
 */
function search(input, template) {
    try {
        // input is a valid URL:
        // eg: https://example.com, https://example.com/test?q=param
        return new URL(input).toString();
    } catch (err) {
        // input was not a valid URL
    }

    try {
        // input is a valid URL when http:// is added to the start:
        // eg: example.com, https://example.com/test?q=param
        const url = new URL(`http://${input}`);
        // only if the hostname has a TLD/subdomain
        if (url.hostname.includes('.')) return url.toString();
    } catch (err) {
        // input was not valid URL
    }

    // input may have been a valid URL, however the hostname was invalid

    // Attempts to convert the input to a fully qualified URL have failed
    // Treat the input as a search query
    return template.replace('%s', encodeURIComponent(input));
}