JavaScript is an Object-Oriented Language (OOL).

Object: A "thing," like the window or a form or a button (on the screen).

Property: Objects have properties. For example, the window has a name, the form may have a target or a textbox.

Method: Methods are what the objects can do. For example, the window may be open, a button may be clicked. Parentheses follow methods, so if there's a set of parentheses, the item to its left has to be a method.

Objects, properties, and methods are separated by periods (or dots); this is called dot syntax. Here are some examples:
document.image.linkcolor (object and two properties)
document.write() (object and method)
form.elements.Text.click() (object, 2 properties, and a method)
Objects and properties can be thought of as nouns, with methods being the verbs.

Values: There are six value types. You're probably most familiar with the number type. 5.48 is a numeric value. But to the computer, a string (text) is another kind of value.

Variables: Variables contain values. You can think of it like a small rural Post Office. Mail is stored in boxes corresponding to addresses. In the computer, a variable name (such as PI) would be the name of the "box" - that's the location in the memory - where 3.1416 is stored. PI, for example, would be a variable name. 3.1416 is the value.

Assignment Statements and Operators: To assign a value to a memory location, the equals sign is used...

A=2; define memory location A and put the value of 2 in it
B=5; define memory location B and put the value of 5 in it
product=A*B; define memory location product, take the values stored in A and B, multiply them, and put them in location product
word="This is a sentence"; define memory location word and put the string value "This is a sentence" in it.

Semicolons are part of the syntax which will be covered later. A, B, product, and word are variable names. Variable names can't contain spaces or be one of JavaScript's reserved words. But the value, if it is a string, can contain any characters (even blanks). The asterisk is one of the operators - it means "multiply."

Loops: The instructions within a loop are executed until a condition is satisfied. For example...

for (i=0; i<3; i++) {
A=A+5
}
Supposing that A has the value of 2 initially, the for loop sets i to zero, tests it against the condition (i is less than 3), does the instruction (adds 5 to A, getting 7), increments i by one (that's the function of the "i++"), and repeats the process. Can you see that, when the loop is exited, A has 17 stored in it? Here's the execution of the program. Here's the text file, since you can't see the JavaScript portion by using View|Source in your browser. You probably noticed that it's the statement(s) within the curlicues that gets executed. If there's more than one statement to be executed, semicolons separate the statements. See this program's execution for an example (text here). A while loop can be used to do the same thing as the first program, but the counter has to be incremented within the body. The advantage of the while loop is that the incrementation doesn't have to be limited to one.  See the text of this program here.

Comments:

one-line comments start with a double slash
// This is a one-line comment
/* This begins a multi-line comment
*/ This ends a multi-line comment
Here's an illustration of this, as well as the use of:
· text as a string variable
· the write method of the document object
Here's the text form of the illustration program.

A function is a group of statements to do a particular task. Here's an example (text is given here) that displays a button (that says "Hi") which, when clicked (onClick event handler) displays an alert box which says "hello." Functions are followed by parentheses; the item(s) in parentheses are the variables being passed to the function. In this example, the function "sayhello" has no arguments, but the parentheses are still required. What the function is to do is contained within the curlicues; in this case, it calls up an alert box. The function definition is within the HTML document heading.

It is in the body of the HTML document that the function is called. Usually, event handlers are used to do this, and in this case, the onClick event handler is being used. HTML coding is being used to define a button and print "Hi!" on it. The onClick="sayhello()" portion of the INPUT statement is used to call the function when the button is clicked.

In this example, you can see how a different message is passed to "msg". Look at the text here.  There are three buttons and therefore three INPUT statements.  You should notice that single quotes are used in each of the three calling statements because they occur inside the double quotes.

As a final example, here's an engineering problem: Find the stress in part of a machine frame.  Here it is in text form.

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Java vs. JavaScript differences:

• JavaScript scripts are immediately interpreted in the browser; Java applets are compiled to class files;
• JavaScript can define objects but not classes of objects;
• Object inheritance is not supported in JavaScript;
• JavaScript does not require strong type declarations;
• HTML tags and elements may interact with each other when using JavaScript;
• JavaScript has less overhead.