Sometimes we want some code to only run under certain conditions. The if..else statement is one of the most common ways to affect the control flow.

Since a different blocks of code run under different conditions, the if...else statement is a type of conditional statement.

if...else

The if block of code will run if the condition is true. If the condition is false the else block of code runs.

let varNumber = 1000000;
if (varNumber > 1000) {
    console.log('This number is bigger than 1000');
} else {
    console.log('This number is smaller than or equal to 1000');
}

It is also valid code to run only the if statement. This is common when you just want a piece of code to run under a condition but nothing to happen if the condition is false.

let aUser = 'Rachel';
if (aUser === 'Rachel') {
    console.log('Hi, Rachel!');
}

There is also an option to use an else if clause if you want to evaluate more than one statement before else.

let yourHeightInCentimeters = 170;
if (yourHeightInCentimeters  < 158) {
    console.log('You should buy the extra small bike!');
} else if (yourHeightInCentimeters  < 168) {
    console.log('You should buy the  small bike!');
} else if (yourHeightInCentimeters  < 178) {
    console.log('You should buy the medium bike!');
} else if (yourHeightInCentimeters  < 185) {
    console.log('You should buy the large bike!');
} else if (yourHeightInCentimeters  < 193) {
    console.log('You should buy the extra large bike!');
} else {
    console.log('You should buy the extra extra large bike!');
}