A computer program is a list of "instructions" to be "executed" by the computer.
In a programming language, these program instructions are called statements.
avaScript statements are separated by semicolons:
var x, y, z; x = 5; y = 6; z = x + y;
Values, Operators, Expressions, Keywords, and Comments.
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.
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;
(5 + 6) * 10
var x, y; x = 5; y = 6;/code>
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"
The var keyword tells the browser to create variables:
var x, y; x = 5 + 6; y = x * 10;
Code after double slashes // or between /* and */ 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
You will learn more about comments in a later chapter.
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.
Note: Numbers are not allowed as the first character.
The variables lastName and 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.