Wednesday, August 6, 2008

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.

Labels which refer to a changeable value.
Example: total may be possess a value of 100.
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
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)
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;}
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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