How can I add or update a query string parameter?

Question

With javascript how can I add a query string parameter to the url if not present or if it present, update the current value? I am using jquery for my client side development

Answer 1

I realize this question is old and has been answered to death, but here's my stab at it. I'm trying to reinvent the wheel here because I was using the currently accepted answer and the mishandling of URL fragments recently bit me in a project.

The function is below. It's quite long, but it was made to be as resilient as possible. I would love suggestions for shortening/improving it. I put together a small jsFiddle test suite for it (or other similar functions). If a function can pass every one of the tests there, I say it's probably good to go.

Update: I came across a cool function for using the DOM to parse URLs, so I incorporated that technique here. It makes the function shorter and more reliable. Props to the author of that function.

/**
 * Add or update a query string parameter. If no URI is given, we use the current
 * window.location.href value for the URI.
 * 
 * Based on the DOM URL parser described here:
 * http://james.padolsey.com/javascript/parsing-urls-with-the-dom/
 *
 * @param   (string)    uri     Optional: The URI to add or update a parameter in
 * @param   (string)    key     The key to add or update
 * @param   (string)    value   The new value to set for key
 *
 * Tested on Chrome 34, Firefox 29, IE 7 and 11
 */
function update_query_string( uri, key, value ) {

    // Use window URL if no query string is provided
    if ( ! uri ) { uri = window.location.href; }

    // Create a dummy element to parse the URI with
    var a = document.createElement( 'a' ), 

        // match the key, optional square brackets, an equals sign or end of string, the optional value
        reg_ex = new RegExp( key + '((?:\\[[^\\]]*\\])?)(=|$)(.*)' ),

        // Setup some additional variables
        qs,
        qs_len,
        key_found = false;

    // Use the JS API to parse the URI 
    a.href = uri;

    // If the URI doesn't have a query string, add it and return
    if ( ! a.search ) {

        a.search = '?' + key + '=' + value;

        return a.href;
    }

    // Split the query string by ampersands
    qs = a.search.replace( /^\?/, '' ).split( /&(?:amp;)?/ );
    qs_len = qs.length; 

    // Loop through each query string part
    while ( qs_len > 0 ) {

        qs_len--;

        // Remove empty elements to prevent double ampersands
        if ( ! qs[qs_len] ) { qs.splice(qs_len, 1); continue; }

        // Check if the current part matches our key
        if ( reg_ex.test( qs[qs_len] ) ) {

            // Replace the current value
            qs[qs_len] = qs[qs_len].replace( reg_ex, key + '$1' ) + '=' + value;

            key_found = true;
        }
    }   

    // If we haven't replaced any occurrences above, add the new parameter and value
    if ( ! key_found ) { qs.push( key + '=' + value ); }

    // Set the new query string
    a.search = '?' + qs.join( '&' );

    return a.href;
}