How to write a replacer function to transform values while the JSON.stringify() function is generating the JSON text string?

Below is a good example on using a replacer function with the JSON.stringify() call to transform output values:

<!-- JSON-stringify-Transformed.html
     Copyright (c) FYIcenter.com 
-->
<html>
<body>
<script type="text/javascript">

function transformer(key, value) {
    if (key == "age") {
       return undefined;
    } else if (key == "group" && value==null) {
       return "Guest";
    } else {
       return value;
    }
}

function stringifier(val) {
   var str = JSON.stringify(val,transformer);
   return str;
}

   document.write("
JSON.stringify() Replacer to Transform Values:
");
   document.write("
");

   str = '{"name": "Joe", "age": 25, "group": null}';
   document.write("Input  = "+str+"\n");
   json = stringifier(JSON.parse(str));
   document.write("Output = "+json+"\n");

   str = '{"name": "Jay", "age": 55, "group": "VIP"}';
   document.write("Input  = "+str+"\n");
   json = stringifier(JSON.parse(str));
   document.write("Output = "+json+"\n");

   str = '{"name": "Kim", "age": 30, "group": "Host"}';
   document.write("Input  = "+str+"\n");
   json = stringifier(JSON.parse(str));
   document.write("Output = "+json+"\n");

   document.write("
");

</script>
</body>
</html>

The transformer() is used as the replacer function in the JSON.stringify() call to remove the "age" property, and to provide a default value "Guest" to the "group" property.

Open the above code in a Web browser. You see the following output:

JSON.stringify() Replacer to Transform Values:

Input  = {"name": "Joe", "age": 25, "group": null}
Output = {"name":"Joe","group":"Guest"}
Input  = {"name": "Jay", "age": 55, "group": "VIP"}
Output = {"name":"Jay","group":"VIP"}
Input  = {"name": "Kim", "age": 30, "group": "Host"}
Output = {"name":"Kim","group":"Host"}

⇒ JSON-stringify-Filter.html - JSON.stringify() Array Replacer

⇐ Call JSON.stringify() with Replacer Function

⇑ Using JSON in JavaScript

⇑⇑ JSON Tutorials