{"id":1243,"date":"2011-05-30T20:21:18","date_gmt":"2011-05-31T01:21:18","guid":{"rendered":"http:\/\/www.wwco.com\/~wls\/blog\/?p=1243"},"modified":"2011-05-30T20:21:18","modified_gmt":"2011-05-31T01:21:18","slug":"json-and-undefined-properties","status":"publish","type":"post","link":"https:\/\/wls.wwco.com\/blog\/2011\/05\/30\/json-and-undefined-properties\/","title":{"rendered":"JSON and Undefined Object Properties"},"content":{"rendered":"

When are JSON.parse()<\/tt> and JSON.stringify()<\/TT> not inverses of each another?<\/p>\n

Here’s when.<\/p>\n

In JavaScript it’s possible to define an object that has an undefined property:<\/p>\n

var o = {\n    a: \"Hello\",\n    b: undefined\n};<\/code><\/pre>\n
It’s then possible to iterate over all the objects properties and see the values as well.<\/p>\n
for (var p in o) {\n    alert( p + \": \" + o[p] );\n}<\/code><\/pre>\n
This will show “a: Hello” and “b: undefined”.<\/p>\n
Now, to JSON-ify the object and reconstitute it back.
\no = JSON.parse( JSON.stringify(o) );<\/code><\/p>\n
Doing the for-loop again will reveal the object now only has the “a” property (the value is still “Hello”).<\/p>\n
Try it.<\/A><\/p>\n
While I get it, I’m not sure I like it.  Ideally, I’d like anything coming out of JSON<\/a> to be the same as anything going into it.<\/p>\n
Assume this object:<\/p>\n
var me = {\n    mySiblingsGender: undefined\n};<\/code><\/pre>\n
This is one of those cases where several subtleties rear their head on edge cases.<\/p>\n
First, a known value for mySiblingsGender<\/code> might be male<\/code> or female<\/code>.  A null<\/code> would indicate there is no gender, perhaps by a horrible vegetable peeler accident<\/a>.  (Oh my!)  But an undefined<\/em> value indicates there is one, we just don’t know what it is.<\/p>\n
Removing the property completely instead conveys that there is no sibling (absence) — something totally different than null (not having any) or undefined (unknown).<\/p>\n
While it’s splitting hairs, if not kindling for religious coding wars, it’s useful to know that JSON-out may not always be the same as JSON-in.<\/p>\n","protected":false},"excerpt":{"rendered":"
Ran into an interesting case where the JavaScript object coming out of JSON wasn’t the same as the JavaScript object encoded going in.<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[62,128,86],"tags":[345,354,355,373,406,407,572,578,633,634,716,736,852,853,903,969],"class_list":["post-1243","post","type-post","status-publish","format-standard","hentry","category-geek","category-javascript","category-programming","tag-data","tag-decode","tag-decoding","tag-deserialize","tag-encode","tag-encoding","tag-javascript-2","tag-json","tag-marshal","tag-marshaling","tag-parse","tag-pickle","tag-serialization","tag-serialize","tag-stringify","tag-unpickle"],"_links":{"self":[{"href":"https:\/\/wls.wwco.com\/blog\/wp-json\/wp\/v2\/posts\/1243","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wls.wwco.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wls.wwco.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wls.wwco.com\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/wls.wwco.com\/blog\/wp-json\/wp\/v2\/comments?post=1243"}],"version-history":[{"count":0,"href":"https:\/\/wls.wwco.com\/blog\/wp-json\/wp\/v2\/posts\/1243\/revisions"}],"wp:attachment":[{"href":"https:\/\/wls.wwco.com\/blog\/wp-json\/wp\/v2\/media?parent=1243"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wls.wwco.com\/blog\/wp-json\/wp\/v2\/categories?post=1243"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wls.wwco.com\/blog\/wp-json\/wp\/v2\/tags?post=1243"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}