Transform Arrays with Map() Method

by | Mar 19, 2023 | CentOS 7, Cloud Hosting, JavaScript, Linux Server, VPS Servers, Web Hosting

How to Transform Arrays using JavaScript Map() Method

The map() Method in JavaScript

The map() method in JavaScript allows you to apply a function to each element of an array, creating a new array with the transformed values.

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In this article, we try to discuss some JavaScript Questions like How to convert an array to a map, What the map () array method does, How do you use the map() function, Transform Arrays with Map() Method, How to Transform Arrays using Map() Method, Why Use the map() Method, The map() Method in JavaScript, The Array.map() Method with Callback Functions, JavaScript Array map() Method: Transforming Array Elements, JavaScript map() Method: How to Transform Arrays, How to Transform Arrays using JavaScript Map() Method.

JavaScript Map() Method: How To Transform Arrays

In JavaScript, we can use Array.map() method for Taking an existing array, Applying an operation for each element of the array, and Getting a new array with modified elements.

For instance, given an array of numbers, we can do a new array of the numbers squared given code below

const numbers = [1, 2, 3, 4, 5]
const squared = numbers.map(num => num * num)
console.log(squared)

Output:

[1, 4, 9, 16, 25]
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Why Use the map() Method?

In JavaScript, we can use the map() method to make our code shorter and more summarized.

The map() method lets you replace some lengthy loops with good-looking shorthand statements.

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The map() Method in JavaScript

In JavaScript, the Array.map() method calls a function for each element in an array and the result is a new array with new transformed values.

So, we can start by looking at the syntax of the map() method.

The Array.map() Method with Callback Functions

In this case, the most basic way to use the map() method is by passing it a callback function.

For instance, we can do square an array of numbers.

const numbers = [1, 2, 3, 4, 5]
function square(number) {
return number * number
}
const squared = numbers.map(square)
console.log(squared)

Output:

[1, 4, 9, 16, 25]

The Array.map() Method with Inline Callback Functions

In this method, the word “inline” refers to a function used in the line of code where it is implemented and we called the map() method with a callback function that was defined separately.

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However, we can also define the callback inline when calling the map() method and this means you implement the function without a name right in the map() method call.

For example, we can do square an array of numbers:

const numbers = [1, 2, 3, 4, 5]
const squared = numbers.map(function(number) {
return number * number
})
console.log(squared)

Output:

[1, 4, 9, 16, 25]

The Array.map() Method with Arrow Functions

An arrow function is a shorthand alternative for a traditional function expression and we cannot always use an arrow function.

To keep it short, we did not go to list the arrow function limitations here. Instead, we can check them here.

So, arrow functions can be used with the following below syntaxes:

const numbers = [1, 2, 3, 4, 5]
const squared = numbers.map(num => num * num)
console.log(squared)

Output:

[1, 4, 9, 16, 25]

Example Use Cases for the map() Method

Last but not least, let’s take a look at some examples of how to use the map() method.

Call a Function for Each Element in an Array for map()

You can use the map() method to transform one array into another by calling a function for each element in the array.

For instance, we can create a new array with the strings in the upper case.

const names = ["Alice", "Bob", "Charlie"]
const capsNames = names.map(name => name.toUpperCase())
console.log(capsNames)

Output:

["ALICE", "BOB", "CHARLIE"]

Reformat Array Objects

The map() method can be used when working with arrays of objects as well.

const users = [
{ name: 'Bob', hobby: 'Jogging' },
{ name: 'Charlie', hobby: 'Gym' },
{ name: 'Alice', hobby: 'Golf' }
]
const capsData = users.map(user => {
const userData = {}
userData.name = user.name.toUpperCase()
userData.hobby = user.hobby.toUpperCase()
return userData
})
console.log(capsData)

Output:

[{
hobby: "JOGGING", name: "BOB"
}, {
hobby: "GYM", name: "CHARLIE"
}, {
hobby: "GOLF", name: "ALICE"
}]

Convert String to an Array of Characters

The map() method is known to belong to the Array data type.

However, we can extract this method from the Array, also use it on a string.

To do this, use the .call() method.

The .call() method lets you use the context of one object for another. In this case, you can use the map() method that belongs to an Array on a String.

const name = "Sam"
const arr = Array.prototype.map.call(name, letter => letter.toUpperCase())
console.log(arr)

Output:

["S", "A", "M"]

Conclusion

Today you learned how to use the map() method in JavaScript and the map() method we can be used to transform one array into another.

In each of these examples, the map() method transforms the elements of an array in a specific way to create a new array with the transformed values.

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