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Javascript Essentials 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!'); //--> </script> Save and Browse * Javascript Basics • • Data “Types” • Declarations • Expressions Data Storage Javascript Data Types String - default type Integral -ordinal numbers -Use parseInt() Floating -real numbers -Use parseFloat() Characters and Integers 01000010 char (1 Byte) 256 possibilities, ASCII characters enclosed in single quotes: ‘B’ 01000001 01000001 int (2 or 4 Bytes) no decimal points no commas no special signs ($, ¥, ‰) *** 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 *** Variables / / a place to store information contents of a location in memory / has an address in RAM / uses a certain number of bytes Name num1 Type int Location 1000 1000 -9999 * Identifiers Valid examples: x num1 num2 c237 index tax_rate name row Not valid: 1num bye[a] tax-rate OK: newPos newpos (beware of this!) tax rate *** Identifiers Rules for Naming Identifiers Can contain digits, letters, underscores NO SPACES Begin identifier name with a letter Limit Identifiers to 20 characters *** 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 **** Variable Definition var identifier_list; var i, k; var taxRate = 0.087; var len = 10, wid =20; <script language =“Javascript”> var name = “Joe”; alert('Welcome to my Web Site!‘+ name); </script> **** Literals & Constants Literals: 'Y', 23.4, -1, "Hello" typed directly into the program as needed ex. y = 23.4 pi = 3.1416 Literal values are stored in anonymous memory addresses by the compiler *** Operators An operator is a symbol that causes the compiler to take an action. Categories: mathematical assignment boolean/logical etc. * Binary Arithmetic Operators addition subtraction multiplication * division / modulus Unary Minus operator: + % x = -3; y = -x; * Arithmetic Operators Increment and Decrement Arithmetic Expressions Syntax operand operator operand Example 7 34 92 345 86 + 15 — * / % 189 31 6.02 3 * Integer Division & Modulus The modulus operator yields the remainder of integer division. 4 3 12 12 0 12/3 14/3 12%3 14%3 4 3 14 12 2 ** Modulus Examples The modulus operator yields the remainder of integer division. 18 17 24 4 12 % % % % % 4 is 2 3 is 2 6 is 0 18 is 4 2.5 error 13 35 24 0 6.0 % % % % % 4 is 1 47 is 35 4 is 0 7 is 0 6 error Requires floating point division! Not the same. **** Operator Precedence Order of Operations () * / + - P M D A S from left to right 8 + 3 * 4 is ? Show associativity to clarify. (8 + 3) * 4 is 44 8 + ( 3 * 4 ) is 20 ** Order of Operations Expression 15 Value 10 / 2 * 3 10 % 3 - 4 / 2 -1 5.0 * 2.0 / 4.0 * 2.0 5.0 5.0 * 2.0 / (4.0 * 2.0) 1.25 5.0 + 2.0 / (4.0 * 2.0) 5.25 ***** Evaluation Trees 10 / 2 * 3 10 % 3 - 4 / 2 i i i i i 5.0 * 2.0 / 4.0 * 2.0 5 * 2 / (4.0 * 2.0) i r r r r r ** Evaluation Trees 5.0 + 2.0 / (4.0 * 2.0) r r r 5.0 * 2.0 / 4.0 * 2.0 r (5 + 2) / (4.0 * 2.0) r i r r r Beware! The asterisk is required to indicate multiplication. valid 5*(8+3) (x-y)*(x+y) invalid 5(8+3) (x-y)(x+y) 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. valid invalid name = “Sue” “sue” = name * 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. * Storage Locations 1. 2. 3. deposit = 234; balance = 1000; balance = balance + deposit; 4a. Look up balance value 4b. Look up deposit value 4c. Add values 4d. Store result in balance * Storage Locations deposit balance 234 100 After assignment: balance = balance + deposit; 234 1234 6 bytes of storage q w e r t y\ Assignment Operators String Concatenation Relational and Boolean Operators Conditional Statement (if)