JavaScript 2.0-The Complete Reference, Second ... - freecodingtutorial

Arrays
An important wrinkle about objects in JavaScript is the composite type Array, which is an object
but generally has different creation and access syntax. An array is an ordered list that can
contain primitive and complex data types. Arrays are sometimes known as vectors or lists in
other programming languages and are actually Array objects in JavaScript. The members of an
array are called elements. Array elements are numbered starting with zero. That is, each
element is assigned an index, a non-negative integer indicating its position in the array. You
can think of an array as a series of boxes labeled 0, 1, 2, and so on. You can place a piece of
data into a box, for example, box 5, and later retrieve that data by accessing the element at
index 5. Individual array elements are accessed by following the array name with square
brackets ([ and ]) containing the desired index. For example, to place a string in array element
5 and then retrieve it, you might write
myArray[5] = "Hamburgers are nice, sushi is better.";
var x = myArray[5];
Individually setting the values of an array as shown here can be rather tedious, and there are
more direct ways to populate an array. Array literals are specified by a comma-separated list of
values enclosed in square brackets. The following defines a new array with four numbers and
one string:
var myArray = [2, 4, 6, 8, "ten"];
If you want to define an array but fill it with values later, you can define an empty array in a
similar manner:
var myArray = [];
Because arrays are really Array objects, you can use the object syntax to declare a new array:
var myArray = new Array();
You can then access the array according to the syntax previously discussed.
At this point, just remember that arrays and objects really aren‘t that different. In fact, the main
differences are that arrays are more focused on order than objects and we use different
notation to access arrays. We‘ll talk quite a bit more about arrays in Chapter 7.
Functions
A function is another special type of JavaScript object, one that contains executable code. A
function is called (or invoked) by following the function name with parentheses. Functions can
take arguments (or parameters), pieces of data that are passed to the function when it is
invoked. Arguments are given as a comma-separated list of values between the parentheses of
the function call. The following function call passes two arguments, a string and a number:
myFunction("I am an item", 67);
The call passes myFunction two things, a string and a number, that the function will use to
perform its task. You should notice the similarity with the method invocation here:
document.write("The value of pi is: ", 3.14);
In this case, the write method of the Document object is invoked to output a string to the
current browser window. Methods and functions are indeed closely related. A simple way to
think about it would be that a function appears to not be associated with an object, whereas a
method is a function that is obviously attached to an object. Interestingly, once you get down
into function and objects, the world gets quite complicated and you‘ll discover that functions are
indeed first-class data types in JavaScript. This means that functions are treated just like any
other non-primitive type. They can be assigned to variables, passed to other functions, and
created or destroyed dynamically. We‘ll talk more about what all this means in Chapter 5.