If else in JavaScript - ECMAScript 2021

In JavaScript, if/else is a conditional statement used to execute a block of code based on certain conditions. Here is how to use it in ECMAScript 2021 with examples:

1. Basic if/else statement:

if (condition) {
   statement1;
} else {
   statement2;
}

The condition is an expression that evaluates to true or false. If the condition is true, statement1 is executed. If the condition is false, statement2 is executed. Here's an example:

let age = 18;
if (age >= 18) {
   console.log("You are an adult");
} else {
   console.log("You are not yet an adult");
}

Output: "You are an adult"

2. Multiple if statements:

if (condition1) {
   statement1;
} else if (condition2) {
   statement2;
} else {
   statement3;
}

Here, we have multiple conditions to check. If condition1 is true, statement1 is executed. If condition1 is false and condition2 is true, statement2 is executed. If both condition1 and condition2 are false, statement3 is executed. Here's an example:

let grade = 80;
if (grade >= 90) {
   console.log("A grade");
} else if (grade >= 80) {
   console.log("B grade");
} else if (grade >= 70) {
   console.log("C grade");
} else {
   console.log("Fail");
}

Output: "B grade"

3. Nested if statements:

if (condition1) {
   statement1;
   if (condition2) {
      statement2;
   }
} else {
   statement3;
}

Here, we have a condition within another condition. If condition1 is true, statement1 is executed and then condition2 is checked. If both condition1 and condition2 are true, statement2 is executed. If condition1 is false, statement3 is executed. Here's an example:

let x = 10, y = 20;
if (x > y) {
   console.log("x is greater than y");
   if (x - y > 5) {
      console.log("The difference is greater than 5");
   }
} else {
   console.log("y is greater than x");
}

Output: "y is greater than x"

These are the basic syntax and types of if/else statements in JavaScript ECMAScript 2021.