Preserving undefined that JSON.stringify otherwise removes

Question

How do I preserve undefined values when doing JSON.stringify(hash)?

Here's an example:

var hash = {   "name" : "boda",   "email" : undefined,   "country" : "africa" };  var string = JSON.stringify(hash);  > "{"name":"boda","country":"africa"}" 

Email disappeared from JSON.stringify.

Answer 1

The JSON spec does not allow undefined values, but does allow null values.

You can pass a replacer function to JSON.stringify to automatically convert undefined values to null values, like this:

var string = JSON.stringify(   obj,   function(k, v) { return v === undefined ? null : v; } ); 

This works for undefined values inside arrays as well, as JSON.stringify already converts those to null.