Tutorial 3: Data Types and Operators

• Section A: Using Data Types
  • Data Types
    • Primitive Types
    • Values returned by typeof() operator
  • Numeric Data Types
  • Boolean Values
  • Strings
    • JavaScript Escape Sequences
    • String Object
  • Arrays
    • Two-dimensional array
    • Array Object
• Section B: Expressions and Operators
  • Expressions
  • Arithmetic Operators
    • Arithmetic Binary Operators
    • Arithmetic Unary Operators
  • Assignment Operators
  • Comparison Operators
  • Logical Operators
  • Operator Precedence
  • Calculator Program

Section A: Using Data Types

Data Types

    The JavaScript language supports primitive data types. Data types that can be assigned only a single value are called primitive data types. It also supports reference, or composite data types, which are collections of data represented by a single variable name. The three reference data types supported by the JavaScript language are functions, objects, and arrays. The collections of data in an object are its methods and properties. Arrays are sets of data represented by a single variable name. The variable name that represents an array is often referred to as an object, or array object.

    Programming languages that require you to declare the data types of variables are called strongly typed programming languages. Strong typing is also known as static typing, since data types do not change after they have been declared. Programming languages that do not require you to declare the data types of variables are called loosely typed programming languages. Loose typing is also known as dynamic typing, since data types can change after they have been declared. JavaScript language is a loosely typed programming language.

changingVariable = "Hello World"; // String
changingVariable = 8; // Integer
changingVariable = 5.367; // Floating-point number
changingVariable = true; // Boolean
changingVariable = null; // null

    Example: Tutorial3Ex1.html

Numeric Data Types

An integer is a positive or negative number with no decimal place. Integer values in JavaScript can range from -9007199254740990 (-2⁵³) to 9007199254740990 (2⁵³).

A floating-point number contains decimal places or is written using exponential notation. Exponential notation, or scientific notation, is a way of writing very large numbers with many decimal places, using a shortened format. Numbers written in exponential notation are represented by a value between 1 and 10 multiplied by 10 raised to some power. The value of 10 is written with an uppercase or lowercase E. Example: 200,000,000,000 as 2.0e11. Floating point values in JavaScript range from approximately between -1.7976931348623157 x 10³⁰⁸ and +1.7976931348623157 x 10³⁰⁸. The decimal numbers of a floating point number are between -5 x 10^-324 and 5 x 10^-324. If the floating point value is exceed the range, its value will be infinity or -infinity.

    Example: Tutorial3Ex1.html

Boolean Values

A Boolean value is a logical value of true or false. JavaScript converts the values true and false to the integer 1 and 0 when necessary. For example, when you attempt to use a Boolean variable of true in a mathematical operation, JavaScript converts the variable to an integer value of 1.

    Example: Tutorial3Ex1.html

Strings

A text string contains zero or more characters surrounded by double or single quotation marks. Empty string (var1 = "") is valid value for string literal and is not considered to be null or undefined.

    Example: Tutorial3Ex1.html

Arrays

An array contains a set of data represented by a single variable name. You can think of an array as a collection of variables contained within a single variable. Each piece of data contained in an array is called an element. You create new arrays by using the new keyword and the Array() constructor function, in the same manner that you instantiate objects from your own custom constructor functions. The numbering of elements within an array starts with an index number of zero (0). The Array object length property returns the number of elements in an array.

Syntax:
var array_var = new Array(); // Declare an empty array_var
var array_var = new Array(2); // Declare array_var with two empty elements (array_var[0] and array_var[1])
array_var[2] = "new_element"; // Add the third element into array_var with the value of "new_element"
var array_var = new Array(5, "text"); // Declare array_var with two elements. array_var[0] has the integer 5
                                                           // and array_var[1] has the string "text". 

Two-dimensional array

The following code creates a two-dimensional array and displays the results.

a = new Array(4)
for (i=0; i < 4; i++) {
	a[i] = new Array(4)
	for (j=0; j < 4; j++) {
		a[i][j] = "[" + i + "," + j + "]"
	}
}
document.write("<BR><BR>")
for (i=0; i < 4; i++) {
	str = "Row " + i + ": "
	for (j=0; j < 4; j++) {
		str += (" " + a[i][j])
	}
	document.write(str, "<BR><BR>")
}

     Example: Tutorial3Ex1.html

Section B: Expressions and Operators

Expressions

An expression is a combination of literal values, variables, operators, and other expressions that can be evaluated by the JavaScript interpreter to produce a result. You can use operands and operators to create more complex expressions. Operands are variables and literals contained in an expression. Operators are symbols used in expressions to manipulate operands.

Examples:

"this is a string variable"    // string literal expression
10                                   // integer literal expression
3.156                              // floating-point literal expression
true                                 // Boolean literal expression
null                                  // null literal expression
employee_number           // variable expression
myNumber = 100;          // this statement is an expression that results in the value 100 being assigned to myNumber

Arithmetic Operators

Assignment Operators

Comparison Operators

Logical Operators

Operator Precedence