The JavaScript if-else statement is used to execute the code whether condition is true or false. There are three forms of if statement in JavaScript.
Conditional statements are used to perform different actions based on different conditions.
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
Table of Contents
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) {
// the body of if
}
Example :
// check if the number is positive
const number = prompt("Enter a number: ");
// check if number is greater than 0
if (number > 0) {
// the body of the if statement
console.log("The number is positive");
}
Output :
Enter a number: 5
The number is positive
Suppose the user entered 5. In this case, the condition number > 0
evaluates to true
. And, the body of the if
statement is executed.
Enter a number: -5
Suppose the user entered –5. In this case, the condition number > 0
evaluates to false
. Hence, the body of the if
statement is skipped.
The else Statement
Use the else
statement to specify a block of code to be executed if the condition is false.
Syntax :
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 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";
}
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