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JavaScript
Grammar
JavaScript
code, much like other programming languages, is made
up of statements which serve to make assignments, compare
values, and execute other sections of code. By and large,
programmers will already be familiar with JavaScript's
usage of variables, operators, and statements. Below
is a chart summarizing the main elements of JavaScript
grammar. Following, we will look at each element in
detail.
| Grammer
... |
|
Variables |
Labels
which refer to a changeable value.
Example: total may be possess a value of 100. |
| Operators |
Actors
which can be used to calculate or compare values.
Example: Two values may be summed using the addition
operator (+); total+tax
Example: Two values may be compared using the greater-than
operator (>); total>200 |
| Expressions |
Any
combination of variables, operators, and statements
which evaluate to some result. In English parlance
this might be termed a "sentence" or even a "phrase",
in that grammatical elements are combined into a
cogent meaning.
Example: total=100;
Example: if (total>100) |
| Statements
|
As
in English, a statement pulls all grammatical elements
together into a full thought. JavaScript statements
may take the form of conditionals, loops, or object
manipulations. It is good form to separate statements
by semicolons, although this is only mandatory if
multiple statements reside on the same line.
Example: if (total>100) {statements;} else {statements;}
Example: while (clicks<10) {statements;} |
| Objects |
Containing
constructs which possess a set of values, each value
reflected into an individual property of
that object. Objects are a critical concept and
feature of JavaScript. A single object may contain
many properties, each property which acts like a
variable reflecting a certain value. JavaScript
can reference a large number of "built-in" objects
which refer to characteristics of a Web document.
For instance, the document object contains properties
which reflect the background color of the current
document, its title, and many more. For a fuller
explanation of the built-in objects of JavaScript,
see the section on "Document Object Model". |
| Functions
and Methods |
A
JavaScript function is quite similar to a "procedure"
or "subroutine" in other programming languages.
A function is a discrete set of statements which
perform some action. It may accept incoming values
(parameters), and it may return an outgoing value.
A function is "called" from a JavaScript statement
to perform its duty. A method is simply a function
which is contained in an object. For instance, a
function which closes the current window, named
close(), is part of the window object;
thus, window.close() is known as a
method. |
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