Conditionals

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Anonymous contributor
Published May 6, 2021Updated Oct 8, 2024
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Conditionals take an expression, which is code that evaluates to determine a value, and checks if it is true or false. If it’s true, the program can be told to do one thing and if it’s false, the program can be told to do another thing.

If Statement

An if statement accepts an expression with a set of parentheses:

  • If the expression evaluates to a truthy value, then the code within its code body executes.
  • If the expression evaluates to a falsy value, its code body will not execute.
const isMailSent = true;


if (isMailSent) {
  console.log('Mail sent to recipient 💌');
}

The output would be:

Mail sent to recipient 💌

Note: if is in lowercase letters. Uppercase letters will generate a JavaScript error.

Else Statement

An else block can be added to an if block or series of if-else if blocks. The else block will be executed only if the if condition fails.

const isTaskCompleted = false;


if (isTaskCompleted) {
  console.log('Task completed');
} else {
  console.log('Task incomplete');
}

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 🌙';
}

Else If Statement

After an initial if block, else if blocks can each check an additional condition. An optional else block can be added after the else if block(s) to run by default if none of the conditionals evaluated to truthy.

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

if (time < 10) {
  greeting = 'Good morning 🌄';
} else if (time < 20) {
  greeting = 'Good day 🌁';
} else {
  greeting = 'Good evening 🌉';
}

Here, the result of greeting will be: Good day 🌁.

Codebyte Example

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What do you think will happen when pH is changed to 7?


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