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

Table 2-1: Basic Terminology of Programming Languages
Name Definition Examples
simply a list of statements. {
alert("Hello there");
}
Keyword A word that is a part of the language itself.
Keywords may not be used as identifiers.
Reserved
Word
A word that might become a part of the
language itself. Reserved words may not be
used as identifiers, although this restriction
is sometimes not strictly enforced.
Language Characteristics
while
do
function
var
class
public
When studying a new programming language it is important to detail its major characteristics,
such as how code is executed, whitespace is interpreted, statements indicated, and so on. This
section covers these basic issues and should be understood before we talk about the various
data types, operators, and statements provided by JavaScript.
Script Execution Order
JavaScript code found in (X)HTML documents is interpreted line by line as it is found in the
page. This means that it is a good idea to put function definitions and variable declarations in
the document head, enclosed by the … tags, if they will be used
throughout the page. Certain code—for example, the bodies of functions and actions
associated with event handlers—is not immediately executed.
Case Sensitivity
JavaScript is case-sensitive. This means that capital letters are distinct from their lowercase
counterparts. For example, if you use the identifiers result, Result, and RESULT in your script,
each identifier refers to a separate, distinct variable. Case sensitivity applies to all aspects of
the language: keywords, operators, variable names, event handlers, object properties, and so
on. All JavaScript keywords are lowercase, so when using a feature like an if statement, you
need to make sure you type if and not If or IF. Because JavaScript uses the ―camel-back‖
naming convention, many methods and properties use mixed casing. For example, the M in the
name of the lastModified property of the Document object must be uppercase; using a
lowercase m will retrieve an undefined value.
The primary implication of case sensitivity is that you should pay close attention to capitals
when defining and accessing variables, when using language constructs like if and while, and
when accessing properties of objects. One typo can change the meaning of your whole script
and require significant debugging effort.
Note One exception to JavaScript’s case sensitivity is Internet Explorer 3. In this particular
browser, client-side objects and properties are case-insensitive. This exception does not
pose a problem for scripts you might write today. It merely means that some older scripts
relying on Internet Explorer’s case insensitivity might not work in modern browsers.
HTML and Case Sensitivity
Under HTML 4 and earlier, element and attribute names are case-insensitive. For example, the
following two tags are equivalent: