JavaScript
If...Else Statements
Conditional
statements are used to perform different actions based on different conditions.
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:
Use if to
specify a block of code to be executed, if a specified condition is true
Use else to
specify a block of code to be executed, if the same condition is false
Use else if
to specify a new condition to test, if the first condition is false
Use switch
to specify many alternative blocks of code to be executed
The if
Statement
Use the if
statement to specify a block of JavaScript code to be executed if a condition
is true.
Syntax
if
(condition) {
block of code to be executed if the
condition is true
}
Note that if
is in lowercase letters. Uppercase letters (If or IF) will generate a
JavaScript error.
Example
Make a
"Good day" greeting if the hour is less than 18:00:
if
(hour < 18) {
greeting = "Good day";
}
The result
of greeting will be:
Good day
»
The else
Statement
Use the else
statement to specify a block of code to be executed if the condition is false.
if
(condition) {
block of code to be executed if the
condition is true
}
else {
block of code to be executed if the
condition is false
}
Example
If the hour
is less than 18, create a "Good day" greeting, otherwise "Good
evening":
if
(hour < 18) {
greeting = "Good day";
}
else {
greeting = "Good evening";
}
The result
of greeting will be:
Good day
»
The else if
Statement
Use the else
if statement to specify a new condition if the first condition is false.
Syntax
if
(condition1) {
block of code to be executed if condition1
is true
}
else if (condition2) {
block of code to be executed if the
condition1 is false and condition2 is true
}
else {
block of code to be executed if the
condition1 is false and condition2 is false
}
Example
If time is
less than 10:00, create a "Good morning" greeting, if not, but time
is less than 20:00, create a "Good day" greeting, otherwise a
"Good evening":
if
(time < 10) {
greeting = "Good morning";
}
else if (time < 20) {
greeting = "Good day";
}
else {
greeting = "Good evening";
}
The result
of greeting will be:
Good day
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