Essentials of Javascript - Cultural View

JSON 103
YAML uses a block-indent syntax to allow formatting of structured data without use of additional characters
(ie: braces, brackets, quotation marks, etc.). Besides giving YAML a different appearance than JSON, this
block-indent device permits the encapsulation of text from other markup languages or even JSON in the other
languages native literal style and without escaping of colliding sigils.
Efficiency
JSON is primarily used for communicating data over the Internet, but has certain inherent characteristics that may
limit its efficiency for this purpose. Most of the limitations are general limitations of textual data formats and also
apply to XML and YAML. For example, despite typically being generated by an algorithm (by machine), parsing
must ironically be accomplished on a character-by-character basis. Additionally, the standard has no provision for
data compression, interning of strings, or object references. Compression can, of course, be applied to the JSON
formatted data (but the decompressed output typically still requires further full parsing by the browser for
recognizable keywords, tags and delimiters).
In practice performance can be comparable to that of similar binary data formats [23] and often depends more on
implementation quality than on the theoretical limitations of formats.
JSONP
JSONP or "JSON with padding" is a complement to the base JSON data format, a usage pattern that allows a page
to request and more meaningfully use JSON from a server other than the primary server. JSONP is an alternative to a
more recent method called Cross-Origin Resource Sharing.
Under the same origin policy, a web page served from server1.example.com cannot normally connect to or
communicate with a server other than server1.example.com. An exception is HTML tags. Taking advantage
of the open policy for tags, some pages use them to retrieve JSON from other origins.
To see how that works, let's consider a URL that, when requested, returns a JSON statement. In other words, a
browser requesting the URL would receive something like:
{"Name": "Cheeso", "Rank": 7}
The Basic Idea: Retrieving JSON via Script Tags
It's possible to specify any URL, including a URL that returns JSON, as the src attribute for a tag.
Specifying a URL that returns plain JSON as the src-attribute for a script tag, would embed a data statement into a
browser page. It's just data, and when evaluated within the browser's javascript execution context, it has no
externally detectable effect.
One way to make that script have an effect is to use it as the argument to a function. invoke( {"Name": "Cheeso",
"Rank": 7}) actually does something, if invoke() is a function in Javascript.
And that is how JSONP works. With JSONP, the browser provides a JavaScript "prefix" to the server in the src URL
for the script tag; by convention, the browser provides the prefix as a named query string argument in its request to
the server, e.g.,
The server then wraps its JSON response with this prefix, or "padding", before sending it to the browser. When the
browser receives the wrapped response from the server it is now a script, rather than simply a data declaration. In
this example, what is received is