What is Map Function in JavaScript? Understand the Basic First 


In this article, we will go ahead and learn what is map function? We will also take a look at some new ECMAScript 6 methods. In javascript new methods are included which is copyWithin() and fill() method. So we will take them later but now just understand What is Map Function?

Using a map function you can manipulate each element in the object. Map function transforms the elements into an array. Using the map function you can perform any operation with the specific element in the object. Map function will not modify array except it create a new one and return it. In the previous article, we learn what is closure. this article will help you to understand this example well.

Wait if this statement is overwhelming then let’s take an example and get understand what is the use of map function then you will completely understand where to use it.

So when you execute this statement you will know the beauty of map function. The second array which is returned by the map function is different. The map function will get each element in the array and multiply them with 2.

But how does this happened?

If you are thinking that the map function does everything for us then do not be in this misconception. Because map function will just give us an access to each array element one by one and return them. The whole thing is done in the map function parentheses. So in the map function parentheses which specified a function which multiplies a variable by 2. So map function will just assume that function argument as an array element and multiply them with two and return a new array for us.

The one more use of map function is filtering the array. You can use the map function to filter array elements. Like this.

Suppose you have a few products in the array. for instance, we will just take two products. Now to filter the product price and product me we will perform the following code.

So when you execute this statement you will get set filter array. The product array contains the name of the product and the price array contain the price of the product. So now I hope you understand and how these things work and how you can use the map function to perform such operations.

New ECMAScript Method copyWithin()

So we will first understand what is the use of copyWithin() method. If I just wanted to explain the use of this method than I can say hey copy within method copy part of an array to another location in the same array and return it.

It means copyWithin() method used to copy an array And overwrite whatever elements are there. Using example you will completely understand what is the basic use of this method.

let’s take a syntax of copyWithin() method.

The first parameter is the required parameter. Use of this parameter is at which to copy the sequence to. The negative value counted from the end. two and three parameters are optional. The second parameter Used to specify at which to start copying the element from.

If this parameter has omitted then the default value will be as you which is zero. The end parameter used to specify at which to end copying an element from. If this parameter is omitted then the default value assume to the array.length. So when copy within method copy array then the size of the array remains same. This method would not change the size of the array.

For example,

Now here the first index refers to the index number where we wanted to start copying the array. And the second argument specifies where we wanted to copy an element from. So from the second index, it means from the third element. So this will print 1345 and to complete the size of the array this will print 5 again.

So in this statement, I will just start from the first index. And copy elements from the second index. Now here we had specified 3rd  parameter also. The third parameter used to specify where you wanted to end the copy from. So it refers to the fourth element in the array that is why this array will just copy we 3rd element to two times and print the remaining array.

 

Fill() Method

In ECMAScript 6 a new method introduce which is fill, which allows you to set any number of elements with a fixed value. In other words, fill method feel all the elements of the array from a start index to the end index with static values. 

The syntax of this method is the following

The first value parameter is the required parameter. The first parameter feels array with static values. The second and the third parameter are optional.

the second parameter specifies where to start from, And the third parameter specifies where to end up.

For example,

That’s it.

I hope using this example you will understand how to use the fill() and copyWithin() method. That is all for this article, we will see you in the next tutorial. In the previous video, we learned what is destructuring arguments. if you wanted to read this article then the link is here.