What is the difference between JSON and Object Literal Notation?
Can someone tell me what is the main difference between a JavaScript object defined by using "Object Literal Notation" and JSON object?
According to a JavaScript book it says this is an object defined by using Object Notation:
var anObject = {
property1 : true,
showMessage : function (msg) { alert(msg) }
};
Why isn't it a JSON object in this case? Just because it is not defined by using quotation marks?
Lets clarify first what JSON actually is. JSON is a textual, language-indepedent data-exchange format, much like XML, CSV or YAML.
Data can be stored in many ways, but if it should be stored in a text file and be readable by a computer, it needs to follow some structure. JSON is one of the many formats that define such a structure.
Such formats are typically language-independent, meaning they can be processed by Java, Python, JavaScript, PHP, you name it.
In contrast, JavaScript is a programming language. Of course JavaScript also provides a way to define/describe data, but the syntax is very specific to JavaScript.
As a counter example, Python has the concept of tuples, their syntax is (x, y) . JavaScript doesn't have something like this.
Lets look at the syntactical differences between JSON and JavaScript object literals.
JSON has the following syntactical constraints:
" ). true false null {"foo":"bar","foo":"baz"} ) produce undefined, implementation-specific results; the JSON specification specifically does not define their semantics In JavaScript, object literals can have
undefined . Knowing that, just be looking at the syntax, your example is not JSON because of two reasons:
But most importantly, to repeat my explanation from the beginning: You are in a JavaScript context. You define a JavaScript object. If any, a "JSON object" can only be contained in a string:
var obj = {foo: 42}; // creates a JavaScript object (this is *not* JSON)
var json = '{"foo": 452}'; // creates a string containing JSON
That is, if you're writing JavaScript source code, and not dealing with a string, you're not dealing with JSON. Maybe you received the data as JSON (eg, via ajax or reading from a file), but once you or a library you're using has parsed it, it's not JSON anymore.
Only because object literals and JSON look similar, it does not mean that you can name them interchangeably. See also There's no such thing as a "JSON Object".
JSON has a much more limited syntax including:
" and not ' There is really no such thing as a "JSON Object".
The JSON spec is a syntax for encoding data as a string. What people call a "JSON Object" ( in javascript ) is really just an ordinary javascript object that has (probably) been de-serialized from a valid JSON string, and can be easily re-serialized as a valid JSON string. This generally means that it contains only data ( and not functions ). It also means that there are no dates, because JSON does not have a date type ( probably the most painful thing about JSON ;)
Furthermore, (side-rant...) when people talk about a "JSON Object", they almost always mean data that has the "curly-braces" at the top-level. This corresponds nicely to a javascript object. However, the JSON spec does not require that there be a single "curly-braces" object at the top-level of a JSON string. It is perfectly valid JSON to have a list at the top-level, or even to have just a single value. So, while every "JSON Object" corresponds to valid JSON, not all valid JSON strings correspond to what we would call a "JSON Object"! ( because the string could represent a list or an atomic value )
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