Constructions if..else in Javascript. Examples

Conditional constructions allow you to perform certain actions depending on certain conditions:

if (condition) {
 actions
}

Let’s consider an example:

var number = 10;//let's create a variable
if (number > 5) {//if the value of our variable is greater than 5, then we execute the code in {}

console.log("Yes");
        
}
//otherwise, this code does nothing

This code can be shortened to:

var number = 10;
if (number > 5) console.log("Yes");

Or like this:

var number = 10;
if (number > 5)
console.log("Yes");

The condition can be difficult:

        var number = 5;
        var age = 18;
        if (number > 2 && age >= 12) {

            console.log("number is more than 5");
            console.log("age is more than 12");
        }

Check if the value exists

        let number = 5;
        if (number) {

            console.log(`So it exists`);
        }

        let number2;
        if (number2) {

            console.log(`Nothing will happen`);
        }

Let’s check whether the variable is declared undefined and whether it is not null:

        if (number !== undefined && number !== null) {
            console.log(`Yes`);
        }

Else

A set of instructions that is executed the if value is false:

        if (Condition) {
            action if condition is true
        }
        else {
            action if condition is false
        }

For example:

       let number = 5;
        if (number = 6) {

            console.log(`This will not work because if = false`);
        } else {
            console.log(`number is definitely not equal to 6`);
        }

You can shorten:

        if (number = 6) console.log(`This will not work because if = false`);
        else console.log(`number is definitely not equal to 6');

Else if

With the else if construct, we can add an alternative condition to the if block:

        const income = 50;
        if (income > 50) {
            console.log("Income over 50");
        }
        else if (income === 50) {
            console.log("Income is 50");
        }
        else {
            console.log("Income less than 50");
        }