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The JavaScript if-else statement is used to execute the code whether condition is true or false. There are three forms of the if statement in JavaScript – these are as follows
- If Statement
- If else statement
- if else if statement
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If statement
This only evaluates the content only if the expression is true. The syntax of the if statement is given below.
Syntax
if ( condition )
{
// statement(s) to be executed
// if condition specified is true
}
A useful example, you can use developer tools in Chrome, Firefox or other browsers to test this out
// check if a number is positive
const number = prompt("Please 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");
}
else Statement
Use the else statement to specify a block of code to be executed if the condition is false.
if (condition)
{
// statements to be executed
// if condition specified is true
}
else
{
// statements to be executed
// if condition specified is false
}
Here is an example of the following
<script>
// check if the number is positive or negative
const number = prompt("Please enter a number: ");
// check if number is greater than 0
if (number > 0)
{
console.log("The number is positive");
}
// if number is not greater than 0
else
{
console.log("The number is either a negative number or 0");
}
</script>
else if Statement
Use the else if statement to specify a new condition if the first condition is false.
if(condition1)
{
// statements to be executed
// if condition1 specified is true
}
else if(condition2)
{
// statements to be executed
// if condition32 specified is true
}
else if(condition3)
{
// statements to be executed
// if condition3 specified is true
}
else
{
//content to be evaluated if no expression is true
}
Here is an example of the above
// check if the number if positive, negative or zero
const number = prompt("Please enter a number: ");
// check if number is greater than 0
if (number > 0)
{
console.log("The number is positive");
}
// check if number is 0
else if (number == 0)
{
console.log("The number is 0");
}
// if number is neither greater than 0 or zero
else
{
console.log("The number is negative");
}