JavaScript if, else, and else if
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
ifto specify a block of code to be executed, if a specified condition is true - Use
elseto specify a block of code to be executed, if the same condition is false - Use
else ifto specify a new condition to test, if the first condition is false - Use
switchto specify many alternative blocks of code to be executed
The switch statement is described in the next chapter.
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:
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:
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:
More Examples
Random link
This example will write a link to either W3Schools or to the World Wildlife
Foundation (WWF). By using a random number, there is a 50% chance for each of the
links.
