6.3 JS Conditions

The if Statement

Use the if statement to specify a block of JavaScript code to be executed if a condition is true.

Syntax

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

Note that if is in lowercase letters. Uppercase letters (If or IF) will generate a JavaScript error.

Example 1: JS The if Statement

Make a "Good day" greeting if the hour is less than 18:00:

if (hour < 18) {
  greeting = "Good day";
}

The result of greeting will be:

Good day

The else Statement

Use the else statement to specify a block of code to be executed if the condition is false.

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

Example 2: JS if .. else part 1

If the hour is less than 18, create a "Good day" greeting, otherwise "Good evening":

if (hour < 18) {
  greeting = "Good day";
} else {
  greeting = "Good evening";
}

The result of greeting will be:

Good day
or
Good evening

The else if Statement

Use the else if statement to specify a new condition if the first condition is false.

Syntax

if (condition1) {
  //  block of code to be executed if condition1 is true
} else if (condition2) {
  //  block of code to be executed if the condition1 is false and condition2 is true
} else {
  //  block of code to be executed if the condition1 is false and condition2 is false
}

Example 3: JS if .. else part 2

If time is less than 10:00, create a "Good morning" greeting, if not, but time is less than 20:00, create a "Good day" greeting, otherwise a "Good evening":

if (time < 10) {
  greeting = "Good morning";
} else if (time < 20) {
  greeting = "Good day";
} else {
  greeting = "Good evening";
}

The result of greeting will be:

Good morning
or 
Good day
or
Good evening