The script tag takes two important attributes −
This function can be used to write text, HTML, or both. Take a look at the following code.
This code will produce the following result −
Whitespace and Line Breaks
Semicolons are Optional
But when formatted in a single line as follows, you must use semicolons −
Note − It is a good programming practice to use semicolons.
Any text between the characters /* and */ is treated as a comment. This may span multiple lines.
var x, y, z; // How to declare variables x = 5; y = 6; // How to assign values z = x + y; // How to compute values
Fixed values are called literals. Variable values are called variables.
The most important rules for writing fixed values are:
Numbers are written with or without decimals:
Strings are text, written within double or single quotes:
"John Doe" 'John Doe'
In a programming language, variables are used to store data values.
var keyword to declare variables.
An equal sign is used to assign values to variables.
In this example, x is defined as a variable. Then, x is assigned (given) the value 6:
var x; x = 6;
/ ) to compute values:
(5 + 6) * 10
= ) to assign values to variables:
var x, y; x = 5; y = 6;
An expression is a combination of values, variables, and operators, which computes to a value.
The computation is called an evaluation.
For example, 5 * 10 evaluates to 50:
5 * 10
Expressions can also contain variable values:
x * 10
The values can be of various types, such as numbers and strings.
For example, "John" + " " + "Doe", evaluates to "John Doe":
"John" + " " + "Doe"
var keyword tells the browser to create variables:
var x, y; x = 5 + 6; y = x * 10;
Code after double slashes
// or between
*/ is treated as a comment.
Comments are ignored, and will not be executed:
var x = 5; // I will be executed // var x = 6; I will NOT be executed
Identifiers are names.
The rules for legal names are much the same in most programming languages.
Subsequent characters may be letters, digits, underscores, or dollar signs.
Numbers are not allowed as the first character.
lastname, are two different variables:
var lastname, lastName; lastName = "Doe"; lastname = "Peterson";
Historically, programmers have used different ways of joining multiple words into one variable name:
first-name, last-name, master-card, inter-city.
first_name, last_name, master_card, inter_city.
Upper Camel Case (Pascal Case):
FirstName, LastName, MasterCard, InterCity.
Lower Camel Case:
firstName, lastName, masterCard, interCity.
Unicode covers (almost) all the characters, punctuations, and symbols in the world.