JavaScript: Get URL Query Argument

Often I have the need to parse the URL query to retrieve the value of a specific named argument. There is no direct way of doing this is JavaScript, so this requires a custom function.

function findQueryArgument (strQuery, strArgumentName) {

    // Valid query?

    if (strQuery) {

        // Split the parameteres

        var arrParameters = strQuery.split("&");

        // Walk through the parameters

        for (var i = 0; i < arrParameters.length; i++) {

            // Get the key/value pair

            var arrPair = arrParameters[i].split("=");

            // Is this the event argument?

            if (arrPair[0] == strArgumentName) {

                // Has value?

                if (arrPair.length > 1) {

                    // Get the value

                    return arrPair[1];

                }

                // Not set

                break;

            }

        }

    }

    // Not found

    return '';

}

The strQuery argument is the full URL query i.e. a=val1&b=val2 etc. The full URL should not be included.
strArgumentName is the name of the argument you're looking for, i.e. a or b.

Please notice that the returned value is URL encoded. To extract the actual string value you need to use the built in JavaScript method unescape.

Here is an example:

// Query string

var strQuery = 'a=val1&b=val2';

// Get the value of the 'b' argument

var strEscaped = findQueryArgument(findQueryArgument, strQuery, 'b');

// Get the unescaped value

var strUnescaped = unescape(strEscaped);

// Display the value

alert(strUnescaped);