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Javascript Syntax
// This is a single-line comment
/*
This is
a multi-line
comment.
*/
Dot Notation
In JavaScript, objects can be referenced using dot notation, starting with the highest-level object (i.e, window). Objects can be referred to by name or id or by their position on the page. For example, if there is a form on the page named "loginform", using dot notation you could refer to the form as follows:
Syntax
window.document.loginform
Assuming that loginform is the first form on the page, you could also refer to this way:
Syntax
window.document.forms[0]
A document can have multiple form elements as children. The number in the square brackets ([]) indicates the specific form in question. In programming speak, every document object contains an array of forms. The length of the array could be zero (meaning there are no forms on the page) or greater. In JavaScript, arrays are zero-based, meaning that the first form on the page is referenced with the number zero (0) as shown in the syntax example above.
Square Bracket Notation
Objects can also be referenced using square bracket notation as shown below.
Syntax
window['document']['loginform']
// and
window['document']['forms[0]']
Dot notation and square bracket notation are completely interchangeable. Dot notation is much more common; however, as we will see later in the course, there are times when it is more convenient to use square bracket notation.
Where Is JavaScript Code Written?
JavaScript code can be written inline (e.g, within HTML tags called event handlers), in script blocks, and in external JavaScript files. The page below shows examples of all three.
Example:
<html>
<body>
<h1>My First Javascript</h1>
<script type="text/javascript">
document.write("Hello!! How are you?");
</script>
</body>
</html>
- JavaScript statements end with semi-colons.
- JavaScript is case sensitive.
- JavaScript has two forms of comments:
- Single-line comments begin with a double slash (//).
- Multi-line comments begin with "/*" and end with "*/".
// This is a single-line comment
/*
This is
a multi-line
comment.
*/
Dot Notation
In JavaScript, objects can be referenced using dot notation, starting with the highest-level object (i.e, window). Objects can be referred to by name or id or by their position on the page. For example, if there is a form on the page named "loginform", using dot notation you could refer to the form as follows:
Syntax
window.document.loginform
Assuming that loginform is the first form on the page, you could also refer to this way:
Syntax
window.document.forms[0]
A document can have multiple form elements as children. The number in the square brackets ([]) indicates the specific form in question. In programming speak, every document object contains an array of forms. The length of the array could be zero (meaning there are no forms on the page) or greater. In JavaScript, arrays are zero-based, meaning that the first form on the page is referenced with the number zero (0) as shown in the syntax example above.
Square Bracket Notation
Objects can also be referenced using square bracket notation as shown below.
Syntax
window['document']['loginform']
// and
window['document']['forms[0]']
Dot notation and square bracket notation are completely interchangeable. Dot notation is much more common; however, as we will see later in the course, there are times when it is more convenient to use square bracket notation.
Where Is JavaScript Code Written?
JavaScript code can be written inline (e.g, within HTML tags called event handlers), in script blocks, and in external JavaScript files. The page below shows examples of all three.
Example:
<html>
<body>
<h1>My First Javascript</h1>
<script type="text/javascript">
document.write("Hello!! How are you?");
</script>
</body>
</html>
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