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

This is not a problem in itself. The problem comes when novice programmers see HTML event
handlers referenced in two different ways (like ONCLICK and onClick in the previous example)
and assume event handlers can be accessed similarly in JavaScript. This is not the case. The
corresponding event handler in JavaScript is onclick, and it must always be referred to as
such. The reason that ONCLICK and onClick work in HTML is that the browser automatically
binds them to the correct onclick event handler in JavaScript.
Consider also the following two tags, which are not equivalent:
The reason they are not equivalent is that the first modifies the variable x, while the second
modifies X. Because JavaScript is case-sensitive, these are two distinct variables. This
illustrates an important aspect of HTML attributes: while the attribute name is not casesensitive,
its value may be. The onclick HTML attribute is not case-sensitive and so may be
written onClick, ONCLICK, or even oNcLiCk. However, because the value to which it is set
contains JavaScript, its value is case-sensitive.
Fortunately, with the rise of XHTML, which requires that element and attribute names be written
in lowercase, the case sensitivity issue at the intersection between the two technologies is less
murky. Developers should always assume case sensitivity and as far as markup goes,
lowercase should always be favored.
Whitespace
Whitespace characters are those characters that take up space on the screen without any
visible representation. Examples include ordinary spaces, tabs, and linebreak characters. Any
sequence of excessive whitespace characters is ignored by JavaScript. For example
x = x + 1;
is the same as
x = x + 1;
This suggests that the use of whitespace is more for the benefit of the programmer than the
interpreter. Indeed, thoughtful use of whitespace to offset comments, loop contents, and
declarations results in more readable and understandable code.
Note Because of JavaScript’s ambivalence to whitespace and most Web users’ frustration with
slow download times, some JavaScript programmers choose to ―compress‖ their scripts
by removing excess whitespace characters either by hand or using a tool.
The spacing between tokens can be omitted if the meaning is unambiguous. For example,
x=
contains no spaces, but is acceptable because its meaning is clear. However, most operations
other than simple arithmetic functions will require a space to indicate the desired meaning.
Consider the following:
s = typeof x;
s = typeofx;