CSIS 138 JavaScript Class2
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This document provides an overview of various JavaScript concepts including: - The prompt() function to get user input and display it. - Mathematical, assignment, increment/decrement, comparison, and logical operators. - How to display alerts for calculations and check if a value is a number using isNaN(). - If, if/else, and if/else if statements for conditional execution of code based on expression evaluations. Examples are given of comparing values and combining comparison and logical operators.
CSIS 138 JavaScript Class2
- 1. JavaScript – Class 2 prompt() operators Calculations if statement
- 2. prompt("Please enter your name", "");
- 3. <head> <script language="JavaScript"> var myPrompt ; myPrompt = prompt("Please enter your name", ""); </script> </head> <body> <script language="JavaScript"> document.write( myPromp t); </script> </body>
- 4. Mathematical operators : + - / * % • Precedence - * and / are performed first unless you use parenthesis Assignment operator: = also assigns a value to a variable Increment and decrement operators: ++ --
- 5. Comparison operators: < <= > >= == != Logical operators: && || ! Commonly used with an “if” statement
- 6. <script language="JavaScript"> alert(1 + 1); </script> <script language="JavaScript"> var firstNumber = 40; var secondNumber = 20; alert(firstNumber + secondNumber); </script>
- 7. NaN – Not a Number a special value in JavaScript that is returned if you do a calculation with a non-number character IsNaN() – function tests if a variable is a number or not – returns a Boolean data type returns true if it is a string (because a string is not a number) returns false if it is a number
- 8. <script language="JavaScript"> alert(isNaN("teresa")); </script> See page 6 in handout
- 9. if statement <script language=“JavaScript”> var variable1 = 123; var variable2 = 123; if ( variable1 == variable2 ) { alert ("condition true"); } </script> no semicolon == means: is the same or is equal or is true the condition to be evaluated is inside the parenthesis code to be executed if the condition is true see page 7 handout
- 10. Using comparison and logical operators <script language=“JavaScript”> var variable1 = 2; var variable2 = 4; var variable3 = 6; if ( ( variable1 < variable2 ) || ( variable2 < variable3 ) ) { alert ("condition true"); } </script> See page 8 and 9 in handout
- 11. if else statement see page 10 handout Gives you the ability to execute code when the condition evaluates to true and also when it evaluates to false if (condition) { code here will execute if condition is true’ } else { code here will execute if condition is false; }
- 12. if else statement see page 10 handout <script language=“JavaScript”> var variable1 = 123; var variable2 = 124; if (variable1 == variable2) { alert ("true"); } else { alert("false"); } </script>
- 13. if else if statement see page 11 handout var variable1 = 123; var variable2 = 124; if (variable1 == variable2) { alert("equal"); } else if (variable1 < variable2) { alert("less than"); } else { alert("none of the above"); } “ else if “block can be repeated as needed
- 14. JavaScript – Class 2 Assignment 2
Editor's Notes
- #2: The JavaScript Language consists of objects CSIS 138 Instructor Teresa Pelkie Class 2 - Summer 2008