Lesson 2

Mastering Conditional and Logical Operators and the forEach Loop in JavaScript


Hello! Today, we're going to dive into some key concepts of JavaScript. We will focus on the ternary conditional operator, logical AND and OR operators, and the forEach loop. What's awesome about these topics is that, although each one is a simple tool on its own, when used together they can significantly streamline your code and enhance its readability. So, whether you're developing interactive web pages, building web apps, or even gaming, mastering these tools will undoubtedly prove beneficial!

Understanding the Ternary Conditional Operator

A Ternary Operator in JavaScript serves as a shortcut for an if-else statement. It derives its name "ternary" from involving three parts: a condition, a true result, and a false result.

Here's how it appears:

1let result = (condition) ? 'value if true' : 'value if false';

If the condition holds true, you receive the first result; otherwise, you obtain the second result.

For instance, consider that you're developing a game and want to set a message based on the player's score:

1let score = 85; 2let message = (score > 50) ? 'Victory!' : 'Try again.'; 3console.log(message); // 'Victory!'

In the example above, the game declares 'Victory!' when the player's score exceeds 50; otherwise, it encourages the player to 'Try again.'.

Let's consider a more complicated example where we use a nested ternary operator. Assume we want to classify a number as "negative", "positive", or "zero":

1let number = 5; 2let description = (number > 0) ? 'positive' : (number < 0) ? 'negative' : 'zero'; 3console.log(description); // 'positive'

In the above example, if number is greater than 0, we get 'positive'. If not, JavaScript checks if number is less than 0, in which case we get 'negative'. If both conditions fail (i.e., if the number is 0), we get 'zero'. We used a nested ternary operator to evaluate a condition in the else block.

Logical AND (`&&`) and OR (`||`) Operators Refresher

In JavaScript, logical operators are utilized to ascertain logic between variables or values. Today, we will examine two such operators: AND (&&) and OR (||).

The AND (&&) operator returns true only if all conditions hold true. This can be beneficial when multiple conditions need to be simultaneously fulfilled. For instance, consider an online store that provides a special discount for customers from a certain region who also have a specific item in their cart:

1let customerRegion = 'North America'; 2let cartContains = 'Special Item'; 3let isDiscounted = (customerRegion === 'North America' && cartContains === 'Special Item'); 4console.log(isDiscounted); // true

Alternatively, the OR (||) operator returns true if at least one of the conditions holds true. This can be useful when an effect has multiple possible triggers. For example, assume that the game sound is activated either when the player clicks on the settings or when the player reaches a particular level:

1let isSettingsClicked = true; 2let isLevelUp = false; 3let activateSound = (isSettingsClicked || isLevelUp); 4console.log(activateSound); // true
Logical AND (&&) and OR (||) Operators with Non-Primitive Values

In JavaScript, logical operators such as AND (&&) and OR (||) can also be used with non-primitive values like objects and arrays.

The AND (&&) operator returns the first falsy value; if not found, it returns the last truthy value. On the other hand, the OR (||) operator returns the first truthy value; if not found, it returns the last falsy value.

Here is an example demonstrating the behavior of AND and OR operators with non-primitive values:

1let firstObject = {name: 'John'}; 2let secondObject = {name: 'Jane'}; 3 4let resultAnd = firstObject && secondObject; 5console.log(resultAnd); // {name: 'Jane'} 6 7let resultOr = firstObject || secondObject; 8console.log(resultOr); // {name: 'John'}

In the above example, since both firstObject and secondObject are truthy, the AND (&&) operator returns the last one (secondObject), while the OR (||) operator returns the first one (firstObject).

Remember, in JavaScript, an empty object is always truthy, while an empty string, null, undefined, NaN, and 0 are falsy. Keep this in mind while dealing with logical operators and non-primitive values. So continuing our work on JavaScript, it's essential to understand how logical operators work, not just for conditional testing, but also for working with non-primitive values. Happy coding!

Practical Use Cases of Logical Operators

Here are a few additional examples illustrating the usage of logical AND && and logical OR || operators with non-primitive JavaScript values.

  • Using Logical AND to Prevent Errors
1let text; 2let message = text && text.length; 3console.log(message); // undefined

In this example, since text is undefined (a falsy value), the && operator doesn't even evaluate text.length (which would cause an error) and directly returns undefined.

  • Setting Default Values with Logical OR
1let currentUser = null; 2let defaultUser = "Guest"; 3let name = currentUser || defaultUser; 4console.log(name); // Guest

Here, if currentUser is falsy (null in this case), defaultUser gets assigned to name.

  • Combining Logical AND and Logical OR
1let server; 2let local = "Local User"; 3let user = server || local && local.toUpperCase(); 4console.log(user); // LOCAL USER

In this example, the && operation is executed first, and then the || operation. So, local.toUpperCase() gets executed if local is truthy, and only if server is falsy does the entire expression evaluate to the result of local.toUpperCase(). Note that the toUpperCase function is used to convert all the string characters to uppercase.

The above examples demonstrate the power and versatility of using logical operators in JavaScript with non-primitive values. It's an efficient way to handle default values and prevent errors caused by undefined or null values.

The `forEach` Loop

In JavaScript, the forEach loop presents an elegant and straightforward method for executing a function for each item in an array.

Here's an example in which we're developing an interactive quiz game and wish to display each question to the player:

1let questions = ["What's your name?", "What's your favorite game?", "Who's your favorite character?"]; 2questions.forEach(function(question) { 3 console.log(question); 4});

In the example above, the forEach method executes the function for every item in the questions array and logs each question in the console.

Lesson Summary

Today, we unveiled the potency of the ternary conditional operator for creating neat and efficient if-else statements, the logical AND and OR operators for complex condition processing, and the forEach loop for hassle-free iteration over arrays.

We're sure you're excited to test these new skills! So, brace yourself because we've got some exciting hands-on practice exercises lined up for you in the next section. We've intricately designed these exercises to reinforce what you've learned and offer you a feel for using these tools in authentic coding scenarios. Happy coding!

Enjoy this lesson? Now it's time to practice with Cosmo!

Practice is how you turn knowledge into actual skills.