Adding a parameter to the URL with JavaScript

Question

In a web application that makes use of AJAX calls, I need to submit a request but add a parameter to the end of the URL, for example:

Original URL:

Answer 1

It handles such URL's:

• empty
• doesn't have any parameters
• already have some parameters
• have ? at the end, but at the same time doesn't have any parameters

It doesn't handles such URL's:

• with fragment identifier (i.e. hash, #)
• if URL already have required query parameter (then there will be duplicate)

Works in:

• Chrome 32+
• Firefox 26+
• Safari 7.1+

function appendQueryParameter(url, name, value) {
    if (url.length === 0) {
        return;
    }

    let rawURL = url;

    // URL with `?` at the end and without query parameters
    // leads to incorrect result.
    if (rawURL.charAt(rawURL.length - 1) === "?") {
        rawURL = rawURL.slice(0, rawURL.length - 1);
    }

    const parsedURL = new URL(rawURL);
    let parameters = parsedURL.search;

    parameters += (parameters.length === 0) ? "?" : "&";
    parameters = (parameters + name + "=" + value);

    return (parsedURL.origin + parsedURL.pathname + parameters);
}

Version with ES6 template strings.

Works in:

• Chrome 41+
• Firefox 32+
• Safari 9.1+

function appendQueryParameter(url, name, value) {
    if (url.length === 0) {
        return;
    }

    let rawURL = url;

    // URL with `?` at the end and without query parameters
    // leads to incorrect result.
    if (rawURL.charAt(rawURL.length - 1) === "?") {
        rawURL = rawURL.slice(0, rawURL.length - 1);
    }

    const parsedURL = new URL(rawURL);
    let parameters = parsedURL.search;

    parameters += (parameters.length === 0) ? "?" : "&";
    parameters = `${parameters}${name}=${value}`;

    return `${parsedURL.origin}${parsedURL.pathname}${parameters}`;
}