2. Javascript Essentials

3. How do I write it??  Start Homesite  Between the start and end BODY tags type:  <script language =“Javascript”  <!-- hide script from old browsers  alert('Welcome to my Web Site!');  //-->   Save and Browse *

4. Data “Types” Declarations Expressions Data Storage Javascript Basics

5. Javascript Data Types  String  Integral  Floating - default type -ordinal numbers -Use parseInt() -real numbers -Use parseFloat()

6. Characters and Integers  char(1 Byte) 256 possibilities, ASCII characters enclosed in single quotes: ‘B’  int (2 or 4 Bytes) no decimal points no commas no special signs ($, ¥, ‰) * * * 01000010 01000001

7. Floating Point Number Data Types  Floating point numbers: signed or unsigned with decimal point  Types: differ in amount of storage space; varies with machine   float (single precision)  double  long double * * *

8. Variables   a place to store information  contents of a location in memory  *  has an address in RAM  uses a certain number of bytes -9999 1000 Name Type Location num1 int 1000

9. Identifiers  Valid examples:  xnum1num2 name rowc237indextax_rate * * * Not valid: 1num bye[a] tax-rate tax rate OK: newPos newpos (beware of this!)

10. Identifiers

11. Rules for Naming Identifiers  Can contain digits, letters, underscores  NO SPACES  Begin identifier name with a letter  Limit Identifiers to 20 characters * * *

12. Variable Definition  Associates an identifier with its use  Can be done with an assignment  or must be done with documentation Identifiers should have meaningful names. - Reduces confusion - Very few one letter names are acceptable: i, j, k, l, x, y, z (others?) - Two letter names? PI * *

13. Variable Definition  var identifier_list;  var i, k;  var taxRate = 0.087;  var len = 10, wid =20; * * var name = “Joe”; alert('Welcome to my Web Site!‘+ name);

14. Literals & Constants Literals: 'Y', 23.4, -1, "Hello" typed directly into the program as needed ex. y = 23.4pi = 3.1416  Literal values are stored in anonymous memory addresses by the compiler * * *

15. Operators  An operator is a symbol that causes the compiler to take an action. * Categories: mathematical assignment boolean/logical etc.

16. Binary Arithmetic Operators  addition+  subtraction   multiplication *  division /  modulus % Unary Minus operator: x = -3; y = -x; *

17. Arithmetic Operators

18. Increment and Decrement

19. Arithmetic Expressions Syntax operand operator operand  Example 7+15 34— 189 92 *31 345 / 6.02 86 % 3 *

20. Integer Division & Modulus 12/3 14/3 12%3 14%3  The modulus operator yields the remainder of integer division. * 4 3 12 12 0 4 3 14 12 2

21. Modulus Examples  The modulus operator yields the remainder of integer division.  18 % 4 is 2 13 % 4 is 1 17 % 3 is 2 35 % 47 is 35 24 % 6 is 0 24 % 4 is 0 4 % 18 is 4 0 % 7 is 0 * * Requires floating point division! Not the same. 12 % 2.5 error 6.0 % 6 error

22. Operator Precedence

23. Order of Operations 8 + 3 * 4 is ?  Show associativity to clarify. ( 8 + 3 ) * 4 is 44 8 + ( 3 * 4 ) is 20 * P M D A S from left to right ( ) * / + -

24. Order of Operations  Expression Value 10 / 2 * 3 10 % 3 - 4 / 2 5.0 * 2.0 / 4.0 * 2.0 5.0 * 2.0 / (4.0 * 2.0) 5.0 + 2.0 / (4.0 * 2.0) 15 5.0 1.25 5.25 * * * * *

25. Evaluation Trees i i 10 / 2 * 3 * 10 % 3 - 4 / 2 i i i 5.0 * 2.0 / 4.0 * 2.0 r r r 5 * 2 / (4.0 * 2.0) i r r

26. Evaluation Trees 5.0 * 2.0 / 4.0 * 2.0 5.0 + 2.0 / (4.0 * 2.0) (5 + 2) / (4.0 * 2.0) i r r r r r r r r

27. Beware!  The asterisk is required to indicate multiplication.  validinvalid 5*(8+3) 5(8+3)  (x-y)*(x+y) (x-y)(x+y)

28. Assignment Operator The assignment operator (=)causes the operand on the left to take on the value to the right side of the statement.  This operator assigns from right to left. validinvalid name = “Sue”“sue” = name *

29. Assignment Statement Syntax:variable = expression;  Examples: quiz1score = 14; lname = “Newman”; fname = “Alfred E.”; wname = fname + “ “ + lname; Do NOT use the word equals here. Use is assigned to or gets. *

30.  4a. Look up balance value 4b. Look up deposit value 4c. Add values 4d. Store result in balance * Storage Locations 1. deposit = 234; 2. balance = 1000; 3. balance = balance + deposit;

31. Storage Locations q e 234 234 2 3 4 100 1234 1234 w 6 bytes of storage deposit balance After assignment: balance = balance + deposit; r t y\

32. Assignment Operators

33. String Concatenation

34. Relational and Boolean Operators

35. Conditional Statement (if)