How JSON.stringify() behaves on JavaScript objects?

When processing an object, JSON.stringify() behave depending on the type of objects based on the following rules:

• Boolean, Number, and String objects are converted to the corresponding primitive JSON values during stringification.
• Date objects are converted JSON strings according the ISO standard.
• All other objects are converted JSON objects with their enumerable properties only.
• Functions are removed if inside an object, or converted to "null" if inside an array, or converted to "undefined" if by itself.
• "undefined" are removed if inside an object, or converted to "null" if inside an array, or converted to "undefined" if by itself.

Here is a JavaScript example showing how different types of objects get stringified:

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

function myFunc() {
   return "Hello!";
}
   
   var myObj = new Object();
   myObj.name = "Joe";
   Object.defineProperty(myObj, 'age', {value: 1, enumerable: false});
   Object.defineProperty(myObj, 'type', {value: 'User', enumerable: true});

   var str = null;
   
   document.write("<p>String from JSON.stringify():</p>");
   document.write("<pre>");

   str = JSON.stringify(new String("false"));
   document.write("   String object = "+str+"\n");

   str = JSON.stringify(new Boolean(false));
   document.write("   Boolean object = "+str+"\n");

   str = JSON.stringify(new Date(2006, 0, 2, 15, 4, 5));
   document.write("   Date object = "+str+"\n");

   str = JSON.stringify(myObj);
   document.write("   Object object = "+str+"\n");

   str = JSON.stringify(JSON);
   document.write("   JSON object = "+str+"\n");

   str = JSON.stringify(myFunc);
   document.write("   Function object = "+str+"\n");

   document.write("</pre>");
</script>
</body>
</html>

Save the above code in a file, JSON-stringify-Object.html, and open it in a Web browser. You see the following output:

String from JSON.stringify():

   String object = "false"
   Boolean object = false
   Date object = "2006-01-02T20:04:05.000Z"
   Object object = {"name":"Joe","type":"User"}
   JSON object = {}
   Function object = undefined

⇒ Call JSON.stringify() with Replacer Function

⇐ JSON-stringify.html - JSON.stringify() Example Code

⇑ Using JSON in JavaScript

⇑⇑ JSON Tutorials