CS346 Javascript -3 Module 3 JavaScript Variables

CS346 Javascript -3 Variables  Variable — value stored in computer memory location Represents a value that can be changed anytime Saves time in writing and updating scripts Makes the purpose of the code clearer  Use the reserved keyword var to create variables  Reserved words, or keywords, are part of the JavaScript syntax  Cannot be used for variable names

CS346 Javascript -3 Variables  Variables must begin with a letter, $, or _ Cannot contain any spaces  Variables, like other JavaScript code, are case-sensitive  You can declare multiple variables in a statement by separating them with commas var first=1, second=“two”, third=“three”;

CS346 Javascript -3 Variables  Conventions Use a lowercase letter for the first letter of first word and uppercase for subsequent words myVariable Use _ to separate individual words my_variable

CS346 Javascript -3 Variable Scope  Variable scope can be either global or local  A global variable is declared outside of a function Available to all parts of the program  A local variable is declared inside a function and is only available within the function Arguments within the parentheses of a function are considered local variables

CS346 Javascript -3 Data Types  String eval( ) myValue = eval(“1+2”); parseInt( ) or parseFloat( ) Start = parseInt(document.form.start.value); Number( ) Start = Number(document.form.start.value); String( ) var num = 10; var numStr = String(num); isNaN( ) Num = isNaN(document.form.start.value);  Integer 8 1,  Floating Point e13  Boolean True False  Null

CS346 Javascript -3 Special Characters  Escaping — Displaying special characters Use the backslash ‘\’  HTML Tags Enclosed in Quotes  Escape Sequences \n = New Line \r = Carriage Return \t = Tab \’ = Single Quote \” = Double Quote \\ = Backslash

CS346 Javascript -3 Example  3-1variable.htm 3-1variable.htm