JavaScript Arithmetic
As with algebra, you can do arithmetic with JavaScript variables:
y=x-5;
z=y+5;
You will learn more about the operators that can be used between JavaScript variables in the next chapter of this tutorial.
The assignment operator = is used to assign values to JavaScript variables.
The arithmetic operator + is used to add values together.
y=5;
z=2;
x=y+z;
The value of x, after the execution of the statements above is 7.
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JavaScript Arithmetic Operators
Arithmetic operators are used to perform arithmetic between variables and/or values.
Given that y=5, the table below explains the arithmetic operators:
Operator Description Example Result
+ Addition x=y+2 x=7
- Subtraction x=y-2 x=3
* Multiplication x=y*2 x=10
/ Division x=y/2 x=2.5
% Modulus (division remainder) x=y%2 x=1
++ Increment x=++y x=6
-- Decrement x=--y x=4
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JavaScript Assignment Operators
Assignment operators are used to assign values to JavaScript variables.
Given that x=10 and y=5, the table below explains the assignment operators:
Operator Example Same As Result
= x=y x=5
+= x+=y x=x+y x=15
-= x-=y x=x-y x=5
*= x*=y x=x*y x=50
/= x/=y x=x/y x=2
%= x%=y x=x%y x=0
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The + Operator Used on Strings
The + operator can also be used to add string variables or text values together.
To add two or more string variables together, use the + operator.
txt1="What a very";
txt2="nice day";
txt3=txt1+txt2;
After the execution of the statements above, the variable txt3 contains "What a verynice day".
To add a space between the two strings, insert a space into one of the strings:
txt1="What a very ";
txt2="nice day";
txt3=txt1+txt2;
or insert a space into the expression:
txt1="What a very";
txt2="nice day";
txt3=txt1+" "+txt2;
After the execution of the statements above, the variable txt3 contains:
"What a very nice day"
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Adding Strings and Numbers
Look at these examples:
x=5+5;
document.write(x);
x="5"+"5";
document.write(x);
x=5+"5";
document.write(x);
x="5"+5;
document.write(x);
Try it yourself.
The rule is:
If you add a number and a string, the result will be a string.
Comparison Operators
Comparison operators are used in logical statements to determine equality or difference between variables or values.
Given that x=5, the table below explains the comparison operators:
Operator Description Example
== is equal to x==8 is false
=== is exactly equal to (value and type) x===5 is true
x==="5" is false
!= is not equal x!=8 is true
> is greater than x>8 is false
< is less than x<8 is true
>= is greater than or equal to x>=8 is false
<= is less than or equal to x<=8 is true
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How Can it be Used
Comparison operators can be used in conditional statements to compare values and take action depending on the result:
if (age<18) document.write("Too young");
You will learn more about the use of conditional statements in the next chapter of this tutorial.
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Logical Operators
Logical operators are used to determine the logic between variables or values.
Given that x=6 and y=3, the table below explains the logical operators:
Operator Description Example
&& and (x < 10 && y > 1) is true
|| or (x==5 || y==5) is false
! not !(x==y) is true
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Conditional Operator
JavaScript also contains a conditional operator that assigns a value to a variable based on some condition.
Syntax
variablename=(condition)?value1:value2
Example
greeting=(visitor=="PRES")?"Dear President ":"Dear ";
If the variable visitor has the value of "PRES", then the variable greeting will be assigned the value "Dear President " else it will be assigned "Dear".
Conditional Statements
Very often when you write code, you want to perform different actions for different decisions. You can use conditional statements in your code to do this.
In JavaScript we have the following conditional statements:
if statement - use this statement if you want to execute some code only if a specified condition is true
if...else statement - use this statement if you want to execute some code if the condition is true and another code if the condition is false
if...else if....else statement - use this statement if you want to select one of many blocks of code to be executed
switch statement - use this statement if you want to select one of many blocks of code to be executed
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If Statement
You should use the if statement if you want to execute some code only if a specified condition is true.
Syntax
if (condition)
{
code to be executed if condition is true
}
Note that if is written in lowercase letters. Using uppercase letters (IF) will generate a JavaScript error!
Example 1
<script type="text/javascript">
//Write a "Good morning" greeting if
//the time is less than 10var d=new Date();
var time=d.getHours();
if (time<10)
{
document.write("<b>Good morning</b>");
}
</script>
Example 2
<script type="text/javascript">
//Write "Lunch-time!" if the time is 11var d=new Date();
var time=d.getHours();
if (time==11)
{
document.write("<b>Lunch-time!</b>");
}
</script>
Note: When comparing variables you must always use two equals signs next to each other (==)!
Notice that there is no ..else.. in this syntax. You just tell the code to execute some code only if the specified condition is true.
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If...else Statement
If you want to execute some code if a condition is true and another code if the condition is not true, use the if....else statement.
Syntax
if (condition)
{
code to be executed if condition is true
}
else
{
code to be executed if condition is not true
}
Example
<script type="text/javascript">
//If the time is less than 10,
//you will get a "Good morning" greeting.
//Otherwise you will get a "Good day" greeting.var d = new Date();
var time = d.getHours();
if (time < 10)
{
document.write("Good morning!");
}
else
{
document.write("Good day!");
}
</script>
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If...else if...else Statement
You should use the if....else if...else statement if you want to select one of many sets of lines to execute.
Syntax
if (condition1)
{
code to be executed if condition1 is true
}
else if (condition2)
{
code to be executed if condition2 is true
}
else
{
code to be executed if condition1 and
condition2 are not true
}
Example
<script type="text/javascript">
var d = new Date()
var time = d.getHours()
if (time<10)
{
document.write("<b>Good morning</b>");
}
else if (time>10 && time<16)
{
document.write("<b>Good day</b>");
}
else
{
document.write("<b>Hello World!</b>");
}
</script>
The JavaScript Switch Statement
You should use the switch statement if you want to select one of many blocks of code to be executed.
Syntax
switch(n)
{
case 1:
execute code block 1
break;
case 2:
execute code block 2
break;
default:
code to be executed if n is
different from case 1 and 2
}
This is how it works: First we have a single expression n (most often a variable), that is evaluated once. The value of the expression is then compared with the values for each case in the structure. If there is a match, the block of code associated with that case is executed. Use break to prevent the code from running into the next case automatically.
Example
<script type="text/javascript">
//You will receive a different greeting based
//on what day it is. Note that Sunday=0,
//Monday=1, Tuesday=2, etc.var d=new Date();
theDay=d.getDay();
switch (theDay)
{
case 5:
document.write("Finally Friday");
break;
case 6:
document.write("Super Saturday");
break;
case 0:
document.write("Sleepy Sunday");
break;
default:
document.write("I'm looking forward to this weekend!");
}
</script>
