Hello Trailblazers,

Welcome to the sixth tutorial in JavaScript Tutorial Series by SFDC Stop. In this tutorial, we're going to learn about ES6 classes in JavaScript. We'll see how we used to define classes in JavaScript before ES6 and how easy it is to define a class now using ES6 syntax. We'll also learn about defining private variables in JavaScript classes. This tutorial is published on SFDC Stop YouTube Channel. So, if you want to learn in detail, have a look at the tutorial video down below. Otherwise, you can scroll down to have a look at the code gist with explanation.

Tutorial Video

Code Gist with Explanation

How we used to create a class in JavaScript before ES6?

We're going to define a simple class named as Car. The code for the class is given below:

As you can see above, the class car is defined as a function itself because classses in JavaScript are special functions. It will receive two parameters inside the constructor: name and speed, which are parameters to the car function in the code. These two parameters name and speed are used to initialize two data members of the class with the same name i.e. name and speed. Note that the data members are referred by using this keyword.

After the constructor, we have a function named as showSpeed() which is used to display the speed of the car. This function belongs to the Car class, that is why we've used Car.prototype.<function-name> syntax to define the member function. This function can access the data members of the car by using the this keyword.

After the function definition, we simply created the instance of the car class named as audi and passed the name and speed of the car in the constructor as: audi and 200. Finally, we called our showSpeed() method to display the speed of the car by using the class instance. The output when we run this code is given below:

The code is executed successfully and we're getting the expected result i.e. 200 which is the speed of the car.

How can we now define a class in JavaScript using ES6 syntax?

Using ES6 we can define a class using class keyword and the constructor of the class can be defined using constructor keyword. Let's have a look at the same Car class but this time, it's defined using ES6 as shown below:

As you can see in the above code, this time we've defined a Car class using the class keyword. This syntax is very similar to other programming languages. Inside the class, we've defined a constructor by using the constructor keyword. This constructor is accepting two parameters: name and speed. The two data members name and speed of the class are referred using this keyword inside the constructor and are given the values passed inside the constructor. After that we've a function inside the class itself named as showSpeed() which is responsible to display the speed of the car.

The remaining code snippet is same, we've again created the instance of the Car class named as audi and passed the name and speed of the car in the constructor as: audi and 300. Finally, we called our showSpeed() method to display the speed of the car by using the class instance. The output when we run this code is given below:

As you can see above, we're getting the speed of the car displayed as 300 in the console.

Can we have private variables inside classes in JavaScript?

The answer is YES! You can define private variables inside classes in JavaScript. Let's have a look at the modified code snippet to understand how:

As you can see above, we have added one more parameter to the constructor of our class Car named as: color. This parameter is assigned to a new data member identified by #color which is also declared above in the class. Here # specifies that, the color data member is private. Also note that it's mandatory to declare the private data member in the class body, that's why we've declared it above at line number 3.

We've also created one more member function named as showColor() which is displaying the value of color data member. Below the class, we've added two statements at line number 22 and 23, where we're displaying the name and speed of the car audi by directly accessing the data members outside the class. We can do that because the data members are public and we can access the public data members directly outside the class. However, we also have a commented statement at line 24 where we're trying to access the color data member outside the class.

As we know, that the color data member is private, we cannot access it outside the class. You can give it a try by un-commenting the line and running the code snippet. You'll get an error as shown below:

If we comment that line again and try to access the color using the showColor() function which is called at the last, the code will work fine and you'll get the output as shown below:

So, as you can see above, we're getting the value 300 from showSpeed(), then we're getting the name and speed of the car by directly accessing the public variables outside the class with values: audi and 300. Finally, we're displaying the color of the car by using the showColor() which is displayed as red as it's the same color that we've passed in the constructor of the class.

To summarize, the learnings are given below:-

• Before ES6, we used to define a class by using the syntax of a function because classes in JavaScript are Special Functions. The member functions of the class were defined outside the classs function.
• ES6 made it very simple to define a class using the class keyword. We can define a constructor inside the class as well by using the constructor keyword. The member functions of the class can be defined inside the class body itself.
• We can also define private variables in a class. Private variables must be explicitly declared inside the class body and are prefixed by a #. They can only be accessed inside class member functions.

That's all for this tutorial. I hope you liked it. All the code used in this tutorial is available on GitHub and you can have a look at that by clicking here. Make sure to have a look at the video if you want to learn in detail and let me know your feedback in the comments down below.

Happy Trailblazing..!!

 Hello Trailblazers,

Welcome to the fifth tutorial in JavaScript Tutorial Series by SFDC Stop. In this tutorial, we're going to learn about Spread Operator in ES6. We'll see how we can spread an array into multiple elements using the spread operator and also, how we can combine multiple elements into a single array by using spread operator as a rest parameter in ES6 JavaScript functions. This tutorial is published on SFDC Stop YouTube Channel. So, if you want to learn in detail, have a look at the tutorial video down below. Otherwise, you can scroll down to have a look at the code gist with explanation.

Tutorial Video

Code Gist with Explanation

How we used to pass array elements as parameters inside the function before ES6?

We're going to define a simple JavaScript function which will display the array elements passed as parameters. The code for that function is given below:

As you can see, we're having a function named as eats which has 3 parameters fruit1, fruit2, fruit3 and will print the statement consisting of the values of these. We're passing the fruits array elements into the function as fruits[0], fruits[1] and fruits[2]. The output when we run this code is given below:

How can we now pass array elements into function using spread operator in ES6?

ES6 has defined spread operator and it made it much simpler to pass array elements as parameters to a function in JavaScript. The updated code is given below:

As you can see in the above code, we're passing the array elements to function parameters by using the statement eats(...fruits);. When we specify three dots (...) before an array then it spreads the array into it's elements. That's why this operator is known as the spread operator. Therefore, while passing the array into the eats function, we're spreading it into multiple elements. The output when the above code is executed is given below:

As you can see above, the output is exactly the same as we've seen before.

What are Rest parameters in JavaScript ES6?

We've seen above that the ES6 spread operator (...) can be used to break an array into it's elements. But do you know that we can also use it to combine multiple JavaScript variables into a single array? We can pass multiple parameters to a JavaScript function and we can combine all those parameters to an array by using the spread operator. Let's see how:

As you can see above, we have created a function named as car. It has two parameters: name and features with a spread operator. This features parameter is nothing but an array and we're displaying the features of the car by iterating this array using the forEach loop. You can see above that we've called the car method with different values as: car('Audi', 'Great Speed', 'Good Color', 'Comfort', 'Good Looks');. So, here, the first argument is the car name Audi and is assigned to the name parameter. All the other arguments are car features and are combined together to form the features array by using the spread operator.

This is why we say that the spread operator can also be used as a Rest Parameter because it collects all the extra - rest of the parameters that are passed to a JavaScript function and forms an array. The output of the above code is given below:

As you can see above, all the features of the car are combined in a features array and we're able to display those features.

Concatenating two arrays using Spread Operator

Do you know we can also concatenate two arrays using spread operator? Let's have a look at the below code snippet to understand how:

As you can see in the above code snippet, we've created two arrays: features and moreFeatures. The features array is having 4 entries :- 'Great Speed', 'Good Color', 'Comfort' and 'Good Looks', whereas the moreFeatures array is having 2 entries:- 'Great Mileage' and 'Amazing Design'. We're using Array.push() method on the features array as features.push() which is basically used to push one element at the end of the array but here, we're spreading our moreFeatures array into multiple elements by using the spread operator. Therefore, these elements are then pushed one by one into the features array automatically and both the arrays are combined into the features array.

The output we're getting when the above code snippet is executed is given below:

As you can see above, it's pushing the elements of moreFeatures array into the features array using the push() and we're getting the output as 6, as the total number of elements are now 6. Also, we displayed the features array and it's showing us all the 6 features together. Therefore, we're able to concatenate two arrays using the spread operator. 

The same can be achieved when you're defining the second array as shown in the below code snippet:

As you can see above, we've passed the features array as an array element after the 'Amazing Design' entry while defining the moreFeatures array. We're spreading this array using the spread operator. This means that the moreFeatures array should contain all the elements of the features array after it's own two elements. Let's have a look at the output below as we're displaying the moreFeatures array using console.log() :

As you can see above, the moreFeatures array has all the elements of the features array appended after it's own elements, so, the spread operator is working perfectly fine.

To summarize, the learnings are given below:-

• Before ES6, if we need to pass array elements as parameters to js function, each array element was specified one by one using the index as array[0], array[1], array[2].
• ES6 made it very simple and we can simply pass the whole array as a single parameter by using the spread operator like: ...array
• In case, we're passing passing multiple values to a function we can combine them to an array using the spread operator. The spread operator is called a rest parameter in such a case.
• We can also concatenate two arrays using the spread operator.

That's all for this tutorial. I hope you liked it. All the code used in this tutorial is available on GitHub and you can have a look at that by clicking here. Make sure to have a look at the video if you want to learn in detail and let me know your feedback in the comments down below.

Happy Trailblazing..!!

Hello Trailblazers,

Welcome to the fourth tutorial in JavaScript Tutorial Series by SFDC Stop. In this tutorial, we're going to learn about ES6 Default Parameters in JavaScript Functions. We're going to see how we used to define default parameters before ES6 and how we can do it using ES6 syntax. This tutorial is published on SFDC Stop YouTube Channel. So, if you want to learn in detail, have a look at the tutorial video down below. Otherwise, you can scroll down to have a look at the code gist with explanation.

Tutorial Video

Code Gist with Explanation

We're going to define a simple JavaScript function which will add two values and display the result. The code for that function is given below:

Now, let's run this code once and then we'll learn about the default parameters. The output when we're calling this function with values 3 and 5 is given below:

How we used to define default parameters before ES6?

Now, let's see how we used to define default parameters before ES6. For this, we're going to provide a default value for the parameter b. The updated code is given below:

As you can see in the above code, inside the function we're checking that if b is defined i.e. we're passing a value for parameter b, we're using that b itself otherwise, we're going to assign a default value to b which is 2. The output when the above function is called is given below. This time, we're only going to pass 1 value to the function which will be used for parameter a and the parameter b will take up the default value.

As you can see above, we're passing only one parameter as 3 and the default value 2 is being taken up for parameter b giving us the total sum as 5.

How can we define default parameters using ES6 syntax?

ES6 has made it much simpler to define default parameters for functions in JavaScript. We're going to re-write the same function again now and see how we can define a default value for parameter b using ES6. The updated code is given below:

As you can see above, it is so simple to provide the default value for any parameter in ES6 by just giving that value with an equals = sign. Here we're giving the default value for parameter b as 2 by specifying b=2 in the function parameters itself. The output when the above function is called is given below:

As you can see above, we're getting the output as 5 when the parameters a and b are added as the default value for b is automatically considered as 2 and we're passing the value for a as 3.

How can we define a default value if we're passing an object to a function in JavaScript?

The syntax to define the default value, when an object is passed to a function parameter is given below:

As you can see in the above code snippet, we've defined a function named as personAge which is accepting two parameters, the age of the person and the person object itself. The person object has two properties:- firstName and lastName. We've defined the default value for firstName as Richard and the lastName as Hendricks. Therefore, if this function is called with just one parameter, these values will be taken up as the default values for the person object.

One important thing to notice is that we're assigning an empty object to the person object which has the default values like:- { firstName = 'Richard', lastName = 'Hendricks' } = {}. This is important because we're telling the JavaScript function that the default value for this second parameter as a whole is an empty object which has no values for firstName and lastName, so, the default values for these properties i.e. Richard and Hendricks can be taken up.

The output we're getting when the above function is called is given below:

As you can see above, we've only passed a single value for the age parameter as 20 and we're getting the output as: Richard Hendricks is 20 years old which is perfect. So, this is how you can define default values for an object passed as a parameter to a JavaScript function.

To summarize, the learnings are given below:-

• Before ES6, we were using conditional operator to define the default values for parameters
• ES6 made it very simple and we can simply define a default value for a parameter by providing the value after the = sign at the same place where the parameter is defined
• In case, we're passing an object to the function, we need to define a default value as an empty object after the = sign for the object parameter as a whole. Although, for the object properties, we can define the default values within the parameter definition. Both these steps are important to make sure that the object is initialized as well as the parameters also get their default values.

That's all for this tutorial. I hope you liked it. All the code used in this tutorial is available on GitHub and you can have a look at that by clicking here. Make sure to have a look at the video if you want to learn in detail and let me know your feedback in the comments down below.

Happy Trailblazing..!!