2.2: JavaScript Examples

Overview

The following examples demonstrate data types, arithmetic operations, and input in JavaScript.

Data Types

// This program demonstrates variables, literal constants, and data types.

var n;
var s;
var b;
    
n = 1.23456789012345;
s = "string";
b = true;
    
output("Number n = " + n);
output("String s = " + s);
output("Boolean b = " + b);

// Check the JavaScript environment and write to the console, 
// the current document, or standard output as appropriate.
// Reference: http://progopedia.com/example/hello-world/114/
function output(text) {
  if (typeof console === 'object') {
    console.log(text);
  } 
  else if (typeof document === 'object') {
    document.write(text);
  } 
  else {
    print(text);
  }
}

Output

Number n = 1.23456789012345
String s = string
Boolean b = true

Discussion

Each code element represents:

• • // begins a comment
  • var n, s, and b define variables
  • ; ends each line of JavaScript code
  • i = , d = , s =, b = assign literal values to the corresponding variables
  • output() calls the output function
  • function output(text) defines a output function that checks the JavaScript environment and writes to the console, the current document, or standard output as appropriate.

Arithmetic

// This program demonstrates arithmetic operations.

var a;
var b;
    
a = 3;
b = 2;
output("a = " + a);
output("b = " + b);
output("a + b = " + (a + b));
output("a - b = " + (a - b));
output("a * b = " + a * b);
output("a / b = " + a / b);
output("a % b = " + (a % b));

// Checks the JavaScript environment and writes to the console, 
// the current document, or standard output as appropriate.
// Reference: http://progopedia.com/example/hello-world/114/ 
function output(text) {
  if (typeof console === 'object') {
    console.log(text);
  } 
  else if (typeof document === 'object') {
    document.write(text);
  } 
  else {
    print(text);
  }
}

Output

a = 3
b = 2
a + b = 5
a - b = 1
a * b = 6
a / b = 1.5
a % b = 1

Discussion

Each new code element represents:

• +, -, *, /, and % represent addition, subtraction, multiplication, division, and modulus, respectively.

Temperature

// This program converts an input Fahrenheit temperature to Celsius.

var fahrenheit;
var celsius;
    
output("Enter Fahrenheit temperature:");
fahrenheit = input();

celsius = (fahrenheit - 32) * 5 / 9;

output(fahrenheit.toString() + "° Fahrenheit is " + celsius + "° Celsius");

// Checks the JavaScript environment and reads from the console, 
// the current document, or standard input as appropriate.
function input(text) {
  if (typeof console === 'object') {
    return prompt(text)
  }
  else {
    output(text);
    var isr = new java.io.InputStreamReader(java.lang.System.in); 
    var br = new java.io.BufferedReader(isr); 
    var line = br.readLine();
    return line.trim();
  }
}

// Checks the JavaScript environment and writes to the console, 
// the current document, or standard output as appropriate.
// Reference: http://progopedia.com/example/hello-world/114/ 
function output(text) {
  if (typeof console === 'object') {
    console.log(text);
  } 
  else if (typeof document === 'object') {
    document.write(text);
  } 
  else {
    print(text);
  }
}

Output

Enter Fahrenheit temperature:
 100
100° Fahrenheit is 37.7777777777778° Celsius

Discussion

Each new code element represents:

• function input(text) defines a function that checks the JavaScript environment and reads from the console, the current document, or standard input as appropriate.

References

• Wikiversity: Computer Programming