How to Extract the Value from a URI Query String

Description

URI Query Strings are used to provide page parameters to a web page -- such as an A5W page or HTML page. A specific value for a variable in a query string can be extracted on the client using JavaScript.

Discussion

A URI Query String is a string of variables represented as "name=value" pairs separated by ampersands (&). For example:

var1=alpha&var2=beta&lastname=Smith&firstname=Betty

The value for a specific variable can be extracted using JavaScript to parse the string.

 Parsing a Query String

The following function extracts the value for a specific varname from a query string str:

function getVariableFromURIString(str,varname) {
    var result = "";
    var s = str;
    var indx = s.indexOf(varname+"=");
    if (indx != -1) {
        result = s.split(varname+"=")[1].split("&")[0];
    }
    return result;
}

It can be used as follows to extract the value for a variable named "V.R1.LASTNAME" from a query string that was created using the {dialog.object}.getData() method:

var d = {dialog.object}.getData();
var lastname = getVariableFromURIString(d,"V.R1.LASTNAME");

The same function can be used to extract state variable values from the Grid Component state info object that are fetched using the {grid.object}.getStateInfo() method. For example:

var stateData = {grid.object}.getStateInfo();
//State variable names in the Grid are prefixed with the string "_si2."
var myvar1 = getVariableFromURIString(stateData,"__si2.myvar1");

This is a simple function and does not enforce that the variable name matches. Rather, it assumes that the full variable name has been specified. If one or more variables end with the same string or a variable name ends with the same name as another variable, this method will not work to extract the value from the string. In order to enforce that the entire name matches, you must first convert the query string into an array. Then, you must iterate over each entry in the string and compare the variable name against the variable you want to extract the value for. For example:

function getVariableFromURIString(str,varname) {
    var result = "";
    var s = str;
    s = s.split("&");
    var i = 0;
    for (i = 0; i < s.length; i++) {
        var value = s[i];
        value = value.split("=")
        if (value[0] == varname) {
            // match
            result = value[1];
            break;
        }
    }
    return result;
}

 Decoding Query Strings

You may need to decode the query string. To decode the query string, use the decodeURIComponent() function. For example, suppose you have the following query string and you want to extract the value for "task_name":

task_name=update%20website&percentcomplete=12%25&assigned_to=emp112

The getVariableFromURIString() function above returns the following value:

update%20website

However, note that the spaces in the string are still encoded as "20%". decodeURIComponent() can be used to decode the string to its original value:

var s = decodeURIComponent(value);

After decoding the string, the value is now this:

update website

decodeURIComponent() is a built-in function in the standard JavaScript framework. See the decodeURIComponent() documentation on Mozilla's website to learn more about this function.

If you want to build your own query strings, check out Alpha Anywhere's A5.ajax namespace which includes a number of functions that are useful for building query strings for Ajax Callbacks.

 Referencing a Page Variable in a Client-side Expression

Client side expressions (calc fields, show/hide expressions, enable expressions, conditional image, and conditional style) can refer to session variables if you explicitly 'register' the session variables, as explained in the UI when you define one of these client side expressions.

However, you cannot directly reference a page variable in a client side expression. This section explains how you can do it.

Say you want to hide a control if a page variable called 'var1' is equal to 'alpha'.

  1. Define this show/hide expression:

    A show/hide expression for a field in a UX
    getPageVariable('var1') = 'alpha'
  2. Add this function to Javascript Function Declarations:

    function getPageVariable(varname) {
        var a = new String(window.location);
        a = a.split('?');
        a = a[1].split('&');
        var indx = $u.a.find(a,varname+'=',false,false)
        a=a[indx].split('=')[1];
        return a;
    }

How does this work? It gets the page URL from the window.location object in the browser's DOM, then parses the URL to extract the variable value.