Javascript #2

• A sentence.
• CaSE sEnSItiVE
• each statement (sentence) ends with a semicolon ;

        document.write('hello world');
        alert('yikes');
    

Web browsers have various commands to make things happen called functions . They are like verbs in a sentence.

   alert();

   document.write();
   prompt();

are also a functions. You can identify a function by the use of parenthesis.

Often, you pass an argument to the function inside the parenthesis.

   alert('hello world');

• Numbers
• Strings
• Boolean

  5            // integer numbers
  5.25         // floating point numbers (fractional numbers)
  10.3333333   // floating point numbers 
  -100         // negative integer number
  -2.301       // negative floating point number 

   document.write(5 + 15);

'hello world'    // is a string
"Internet Class" // is a string
'1'              // is a string (not a number)
"as;kl29/P(983a" // is a string
hello world      // is NOT a sting 

// Read "Putting Quotes into Strings" (p28) for details
"Jane said "good day!" to John"    // this is not correct
'Jane said "good day!" to John'    // this is correct
"Jane said \"good day!\" to John"  // this is correct

  true     // special keyword representing a boolean value true
  false    // special keyword representing a boolean value false

Area of the square?

x, and y (which should be familiar to you from Mathematics) are essentially variables

A variable is a container (basket) with a name. In the follwing example, x is a variable

  alert('Hi Bob');

  alert('Hi ' + x); 

  var score;     //declare and name a variable "score"

  var my_score;    // declare
  my_score = 0;    // the symbol "=" means assign. So, assign 0 to "score".

  var your_score = 0;    // declare and assign value
  your_score = 1;        // reuse the variable

/* numbers */
  var myAge = 25;     
  var myTemp = 70.5;  

  /* strings */
  var firstName = 'Peter';
  var lastName = 'Parker';
  var myAddress = "3203 SE Woodstock Ave";
  var myCity = "Portland";

  /* boolean: either true or false (or 1 or 0) */
  var student = true;  

  alert(firstName);   // This will print the string stored - Peter

  alert('firstName'); // Note that this will print the string 'firstName'

  var price = 10;
  var itemsOrdered = 15;
  var totalCost = price * itemsOrdered; 

Note that not all operations are equal. *, /, % take precidence over + and -.

  4 + 5 * 10 // is equivalent to 4 + (5 * 10)

  (4 + 5) * 10

var score = 0;
score = 10;
score = score + 100;  //score will have 110 after this
score = score * 100;  //score will have 11000 after this
score = score / 100;  //score will have 110 after this

socre += 10;  // score = score + 10
score -= 10;  // score = score - 10;
score *= 10;  // score = score * 10;
score /= 10;  // score = score / 10;

score++;      // score = score + 1;    
score--;      // score = score - 1;

var firstName = 'John';
var lastName = 'Smith';
var fullName = firstName + lastName; // JohnSmith

var fullName = firstName + ' ' + lastName // John Smith

Here, the + operator convers the number to a string and concatenate it with the other string. (Otherwise it woudl try to add 10 to a string, which doesn't make sense).

var score = 10;
var message = 'You scored ' + score + ' points.';  // You scored 10 points.

This is called automatic type conversion and can be tricky when adding.

var price = '5'; // user input is usually a string
var shippingCost = 20;

var totalCost = price + shippingCost; // 520

var price = '5'; 
var shippingCost = 20;

var totalCost = +price + shippingCost; // 25

var price = '5'; 
var shippingCost = 20;

var totalCost = Number(price) + shippingCost; //