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JavaScript as a Programming Language
Credit: Kirk Born (St Sci/NASA)
Elements of JavaScript
We will explain JavaScript mostly through examples. We assume that you are familar with "C-like" languages and so will not explain those elements of the language that are similar to "C". Client-Side JavaScript:- Operates on the client-side so it reacts much faster, with more client-side capabilites, and greater security, than other languages
- Is an interpretive langauge, so its basic operation is slower than a compiled language, but is much more flexible and has a more free and easy syntax
- Has a large number of reserved words: the following words are
absolutely, positively reserved:
break false in this void continue for new true while delete function null typeof with else if return varplus about 120 or so words that are sorta reserved or might be reserved in the future. See the complete list in David Flannagan's "JavaScript, the Definitive Guide".
The main components of JavaScript are:
- Expressions and operators: the usual "C-like" with a few exceptions: "new ", "typeof", and "+" used for string concatenation
- Statements: the usual "C-like" statements with a few exceptions: "for (prop in object)...", "with (object)..."
- Strings: declaration, concatenation, length, split, concatenation with numbers, charAt, substring, indexOf. See part [3] Test of Strings
- Functions: these differ in many ways from "C-like" languages. See part [5] Functions and Arguments. for many of the important features of JavaScript dfunctions.
- Classes and objects: these are a major aspect of object-oriented languages, such as JavaScript. See part [4] Test of Objects for many of their features.
- Arrays: these differ from most other languages. See part [2] Test of Arrays for many of their features.
JavaScript, like many languages, makes a distinction between value versus reference, particulary in terms of copies, comparisons, and arguments. Basically, Booleans and numbers are copied, passed, and compared by value, where as all others (object, array, string, function) are copied, passed, and compared by reference (except strings, which are compared by value)
Object Oriented (OO) Programming Concepts
JavaScript is very much an OO type language. The main goals of OO programming are to- Identify classes that group similar entities together
- Create objects from the classes, using the
new Class()
syntax - Populate the classes and objects with variables and functions (called "methods") which describe their behavior
// Define the classes----------------
function Student(year,major,..) {
...
}
function Staff(classification, ...) {
...
}
function Faculty(tenure, research,...) {
...
}
...
// Create the objects for these classes -
for (i = 0; i < n_Students; i++) {
student[i]=new Student(2,"premajor",...)
}
for (i = 0; i < n_Staff; i++ ) {
staff[i]=new Staff("temporary",...) {
}
for (i = 0; i < n_Faculty; i++) {
faculty[i]=new Faculty("tenured",...) {
}
The parameters you pass to the functions that define the class
supply some of the values that define the object. In addition,
you may add functions and other variables both to the classes and to
individual objects to further describe their behavior.
On the other hand, you may decide that, for you specific purposes, staff and faculty should be treated alike, whereas students are to be treated differently. In that case, your division might be FacStaff versus Student.
Class Topics