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Understanding JSON Definition
While writing new episodes for my jQuery Tutorial newsletter many people have asked me
why some variables are defined using quotation marks and why others don’t.
In particular with regard to the animate function example from the previous page, I was asked
the question: Why are there quotation marks around the argument “linear” but not around the
integer whose value is 1500?
We have already talked about the fact that JavaScript function parameters are typeless. This
means that you can pass any type of an argument to them. An argument can be a string (text
enclosed using quotation marks) or an integer (simply a digit.) JavaScript functions parameters
do not determine or ask for the obeject type passed to them like C++ functions do.
The assumed type of the parameter is determined by the programmer, not by the language
specification. This means that when constructing a function of your own you are responsible
for determining the type of the arguments that presumably will be passed to that function.
It’s your responsibility to write the function in such way that handles any possible type of a
parameter passed to it. jQuery programmers made the decision that the first parameter of the
function animate() should be a JSON, the second an integer, and the third a string.
JSON is the syntax rule for defining an object in JavaScript. An object can contain a number of
variables, functions or other objects. Let’s take a look at an incredibly basic example of JSON
object definition:
var obj = { a: 1, b: 2 };
It’s important to note that neither var, nor obj are referred to as JSON. JSON is in itself only a
guideline for object definition in JavaScript as seen between the two { and } brackets. One of
the most important things about JSON is that it uses the : (colon symbol) and the , (comma) to
define the inner contents of an object. In other words, that’s just the way the syntax was defined
by the creators of JavaScript language specification (Originally known as EcmaScript.)
JSON in itself is a unique data representation like var or function. Except it has no keyword
definition. In other words { var a: 1, var b: 2 }; would be a wrong way to create an object and
this would create a JavaScript syntax error. This is important because there is actually a second
way of creating objects in JavaScript using the function keyword where defining a using
var a = 1; would actually be legal, but we will discuss this in another section of this book.
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