Introduction to JavaScript if and else statements

Every day, we make decisions based on certain conditions. For example, we may say, 'If it rains, I will stay inside; if not, I will go outside.' The condition there is the weather. This is one of the decisions we make every single day. Although the decision above is very simple, we make complex decisions sometimes. In this article, you will learn about conditional statements in JavaScript using if and else. The JavaScript if and else statements are one of the JavaScript statements for a beginner to master as part of the fundamentals.

Ok, let's get started!

If

Key Takeaways

• The if is used to execute a block of code if the condition is true.
• else is used to execute a block statement if the if the condition is false
• A block statement can be a statement or a group of statements(for a group of statement, curly brackets are used).
• if and else are all in lowercase letters.
• The default statement (if no other statement is triggered) is undefined if the condition is false.

The condition is what we want to check if it is true or not. This is similar to the JavaScript Boolean value which can possible be of two values : truth or false. If the condition evaluates to be true, the if statement will be executed. If not, the statement will be passed to the next statement. However, if there is no statement to passed on, the default statement will be executed.

the syntax for if statement goes thus:

if (condition){
statement //the block of code to be executed if the condition is true.
}

How if statement works:

You first declare and initialize the variable name. For example:

declare and initialize variable name:

let votingAge = 18;

or

Let say the constitution says 'you are eligible to vote' if you are eighteen (18) and above.

then check if the condition matches the if statement. For example:

if (votingAge >=18){
    console.log ('you are eligible to vote')
}

output:

'You are eligible to vote'

or

However, if the condition is not true, the output will be:

undefined

The undefined is the default value if the condition is not true.

Unless another statement is else or else if is triggered, the default will be undefined.

else

As stated above, the if statement is used to execute a block of code. If the condition is false, the default statement is nothing which is undefined.

let votingAge = 17;

if (votingAge >= 18) //condition
{
console.log('you are eligible to vote'); //statement
}
// the condition is false. The default is undefined (nothing).

However, with else statement, you can write a new block of code to execute if the if condition is false.

else is used to execute another statement to execute.

let votingAge = 17;

if (votingAge >= 18) //condition
{
console.log('you are eligible to vote'); //statement
}
else {
console.log('you are not eligible to vote') //else statement will be executed
}