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Instructor Teresa Pelkie at Palomar College - Variables, Calculations, "if" statement
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JavaScript – Class 2
• prompt()• operators• Calculations• if statement
prompt("Please enter your name", "");
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<head>
<script language="JavaScript">
var myPrompt;
myPrompt = prompt("Please enter your name", "");
</script>
</head>
<body>
<script language="JavaScript">
document.write(myPrompt);
</script>
</body>3
Mathematical operators: + - / * % •
Precedence - * and / are performed first
unless you use parenthesis
Assignment operator: = also assigns a value
to a variable
Increment and decrement operators: ++ --
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Comparison operators: < <= > >= == !=
Logical operators: && || !
Commonly used with an “if” statement
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<script language="JavaScript">
alert(1 + 1);
</script>
<script language="JavaScript">
var firstNumber = 40;
var secondNumber = 20;
alert(firstNumber + secondNumber);
</script> 6
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
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<script language="JavaScript">
alert(isNaN("teresa"));
</script>
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See page 6 in handout
if statement
<script language=“JavaScript”>
var variable1 = 123;
var variable2 = 123;
if (variable1 == variable2)
{
alert ("condition true");
}
</script>9
no semicolon
== means:is the same oris 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
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>10See page 8 and 9 in handout
if else statement
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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; }
if else statement
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see page 10 handout
<script language=“JavaScript”>
var variable1 = 123; var variable2 = 124;
if (variable1 == variable2) { alert ("true"); } else { alert("false"); }
</script>
if else if statement
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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
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JavaScript – Class 2
Assignment 2
