Javascript Card To List

Michael Zippo 04.11.2021

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Programmers like to reduce repetition in their code. The more you repeat your code, the less manageable it is and the slower your programs will run. That is why there are different methods in JavaScript to iterate through datasets.

One of these methods is called the map () method. This method iterates through an existing array and performs a specific function on all the elements of that array.

In this guide we will talk about how to use the JavaScript map () function. We’ll take a look at three common examples of the map () function in action to get you started.

What is the map function ?

The JavaScript map () method calls a specific function on each element of an array. The result of this function is then moved into its own table.

For example, suppose you want to multiply each element in an array by two. You can do this by creating a function that multiplies each element in the array by two and moving that function into a map () method.

The syntax of the map () function is:

function is the callback function that will be executed on each element of the array. To learn more about functions, you can read our ultimate guide to JavaScript functions. thisValue is the default value that will be stored in the function’s this variable. By default, this is not defined.

The map method creates a new array based on the results of the callback function.

The () card has several uses. The most common is to call a function on a list of array elements. An example would be to multiply each number in a list of numbers or find the length of each string in a list of strings.

You will also find the function used to display lists in JavaScript libraries like React or Vue.js.

Calling a function with Map

The map () method allows you to perform a repetitive task on each item in a list, which makes it useful in many cases.

Let’s say you have a store cookie and you will increase the price of each cookie by 5%. Instead of calculating all the new prices individually, you can use the map () method.

Here is the code you would use:

Our code returns:

In this example, we have increased the price of each cookie by 5%. First, we have declared a cookie price list in the "cookiePrices" variable. So we used the map () method with a function that calculates a 5% price increase for each cookie.

"cookie * 1.05" calculated the percentage increase, then we returned that increase, rounded to the nearest two decimal places. Finally, we printed the new table to the console using the console.log () method.

We could also move our function to its function to create our own code. readable:

Our code returns the same values ‚Äã‚Äãas before, but is more readable:

Modify elements to an array

The map () method is often used to modify the elements of an array. Suppose our cookie store is developing a loyalty program for its customers. Each cookie you buy earns you 10 points, and if you earn 100 points you will earn a free cookie.

The following program would allow us to do this:

Our code returns:

In this example, we’ve calculated the total number of points each customer should receive based on the number of cookies they’ve purchased.

First, we have declared a series of objects called " clients ". This list stores the names of our customers and the number of cookies they have purchased using key: value pairs .

So we have declared a function called calculateLoyaltyPoints (). This function adds a new item to each customer item called "points" which is calculated by multiplying the number of cookies each the customer has purchased before 10am.

We use the map () method to scroll through our list of customers and apply our calculateLoyaltyPoints () function Finally, we print the revised list of clients. This list now reflects our " point ‚" value that we added to each customer’s entry.

Render a list using a library

The map () method is commonly used in JavaScript libraries such as React. The purpose of this method is to render the items in a list. Let’s see an example of map () in React.

Say you want to view a list of cookies that our store sells on our website. We could do it using this code:

Map Methods vs. Iterator

Map is an example of an iterator method in JavaScript. These methods allow you to cycle through all the items in a list and perform certain actions.

When deciding to use the map () function, it is a good idea to first ask yourself if another iterator method would be better. Make sure you choose the right one tool for the job.

Here are the other iterator methods that exist in JavaScript:

reduce () : the reduce method allows you to reduce an array to a single value. This method is best if you want to do something like add all the elements in an array.

forEach () : forEach () executes a function on each element of a list. forEach () is similar to for loop in that it allows you to iterate through an array and perform a task on each item.

You might be thinking to yourself, "The map looks a lot like the forEach () method. Are they equal? ‚Äã‚Äã" That’s a good question. There is a subtle difference between these two methods.

The map () function walks through a list, modifying each element of the list and returns a new list, while the forEach () function iterates through a list and, as a side effect, performs certain operations on the list.

The map () function is best used if you need to call a function on every element of a list, declare a list component in a framework like React, or modify the contents of a list.

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