CSIS 138 JavaScript Class2

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Instructor Teresa Pelkie at Palomar College - Variables, Calculations, "if" statement

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  • The JavaScript Language consists of objects CSIS 138 Instructor Teresa Pelkie Class 2 - Summer 2008
  • CSIS 138 JavaScript Class2

    1. 1. JavaScript – Class 2 <ul><ul><li>prompt() </li></ul></ul><ul><ul><li>operators </li></ul></ul><ul><ul><li>Calculations </li></ul></ul><ul><ul><li>if statement </li></ul></ul>
    2. 2. <ul><li>prompt(&quot;Please enter your name&quot;, &quot;&quot;); </li></ul>
    3. 3. <ul><li><head> </li></ul><ul><li><script language=&quot;JavaScript&quot;> </li></ul><ul><li>var myPrompt ; </li></ul><ul><li>myPrompt = prompt(&quot;Please enter your name&quot;, &quot;&quot;); </li></ul><ul><li></script> </li></ul><ul><li></head> </li></ul><ul><li><body> </li></ul><ul><li><script language=&quot;JavaScript&quot;> </li></ul><ul><li>document.write( myPromp t); </li></ul><ul><li></script> </li></ul><ul><li></body> </li></ul>
    4. 4. <ul><li>Mathematical operators : + - / * % • </li></ul><ul><li>Precedence - * and / are performed first </li></ul><ul><li>unless you use parenthesis </li></ul><ul><li>Assignment operator: = also assigns a value </li></ul><ul><li>to a variable </li></ul><ul><li>Increment and decrement operators: ++ -- </li></ul>
    5. 5. <ul><li>Comparison operators: < <= > >= == != </li></ul><ul><li>Logical operators: && || ! </li></ul><ul><li>Commonly used with an “if” statement </li></ul>
    6. 6. <ul><li><script language=&quot;JavaScript&quot;> </li></ul><ul><li>alert(1 + 1); </li></ul><ul><li></script> </li></ul><ul><li><script language=&quot;JavaScript&quot;> </li></ul><ul><li>var firstNumber = 40; </li></ul><ul><li>var secondNumber = 20; </li></ul><ul><li>alert(firstNumber + secondNumber); </li></ul><ul><li></script> </li></ul>
    7. 7. <ul><li>NaN – Not a Number </li></ul><ul><li>a special value in JavaScript that is returned if </li></ul><ul><li>you do a calculation with a non-number character </li></ul><ul><li>IsNaN() – function </li></ul><ul><li>tests if a variable is a number or not </li></ul><ul><li>– returns a Boolean data type </li></ul><ul><li>returns true if it is a string (because a string is not a number) </li></ul><ul><li>returns false if it is a number </li></ul>
    8. 8. <ul><li><script language=&quot;JavaScript&quot;> </li></ul><ul><li>alert(isNaN(&quot;teresa&quot;)); </li></ul><ul><li></script> </li></ul>See page 6 in handout
    9. 9. <ul><li>if statement </li></ul><ul><li><script language=“JavaScript”> </li></ul><ul><li>var variable1 = 123; </li></ul><ul><li>var variable2 = 123; </li></ul><ul><li>if ( variable1 == variable2 ) </li></ul><ul><li>{ </li></ul><ul><li>alert (&quot;condition true&quot;); </li></ul><ul><li>} </li></ul><ul><li></script> </li></ul>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. 10. <ul><li>Using comparison and logical operators </li></ul><ul><li><script language=“JavaScript”> </li></ul><ul><li>var variable1 = 2; </li></ul><ul><li>var variable2 = 4; </li></ul><ul><li>var variable3 = 6; </li></ul><ul><li> </li></ul><ul><li>if ( ( variable1 < variable2 ) || ( variable2 < variable3 ) ) </li></ul><ul><li>{ </li></ul><ul><li>alert (&quot;condition true&quot;); </li></ul><ul><li>} </li></ul><ul><li></script> </li></ul>See page 8 and 9 in handout
    11. 11. <ul><li>if else statement </li></ul>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. 12. <ul><li>if else statement </li></ul>see page 10 handout <script language=“JavaScript”> var variable1 = 123; var variable2 = 124; if (variable1 == variable2) { alert (&quot;true&quot;); } else { alert(&quot;false&quot;); } </script>
    13. 13. <ul><li>if else if statement </li></ul>see page 11 handout var variable1 = 123; var variable2 = 124; if (variable1 == variable2) { alert(&quot;equal&quot;); } else if (variable1 < variable2) { alert(&quot;less than&quot;); } else { alert(&quot;none of the above&quot;); } “ else if “block can be repeated as needed
    14. 14. <ul><li>JavaScript – Class 2 </li></ul><ul><li>Assignment 2 </li></ul>

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