JavaScript Array map() - Apply Function to Elements

Introduction

The map() method in JavaScript is a pivotal tool for array manipulation, allowing you to apply a function to each element in an array and create a new array with the results. This method offers a functional approach to handling arrays and is widely favored for its clarity and efficiency in transforming data.

In this article, you will learn how to effectively harness the map() method across various scenarios. Explore how to transform array elements using simple functions, handle arrays of objects, and integrate map() with other array methods for more complex manipulations.

Basic Usage of map()

Applying Simple Functions to Array Elements

1. Define an array of numerical values.

2. Use map() to create a new array where each value is multiplied by a constant factor.

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   const numbers = [1, 2, 3, 4, 5];
   const multiplied = numbers.map(x => x * 2);
   console.log(multiplied);
   

   This script multiplies each element in the numbers array by 2, resulting in a new array [2, 4, 6, 8, 10].

Convert All Elements to Upper Case

1. Start with an array of strings.

2. Apply map() to convert each string in the array to upper case.

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   const words = ["apple", "banana", "cherry"];
   const upperCased = words.map(word => word.toUpperCase());
   console.log(upperCased);
   

   The map() function processes each string in the words array, turning them into upper case. The output will be ["APPLE", "BANANA", "CHERRY"].

Advanced Manipulation with map()

Processing Arrays of Objects

1. Create an array of objects where each object represents a person with a name and age.

2. Use map() to increase the age of each person by one year and return a new object.

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   const people = [{ name: "Alice", age: 25 }, { name: "Bob", age: 30 }];
   const agedPeople = people.map(person => ({ ...person, age: person.age + 1 }));
   console.log(agedPeople);
   

   Using map(), each person object is processed to return a new object with the age incremented by one. The spread operator (...) ensures that other properties remain unchanged.

Chain map() with Other Methods

1. Utilize map() in conjunction with filter() to manipulate and then filter an array.

2. Create a scenario where you first adjust values and then exclude specific ones.

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   const numbers = [1, 2, 3, 4, 5];
   const filteredNumbers = numbers
       .map(x => x * 3)
       .filter(x => x > 10);
   console.log(filteredNumbers);
   

   This code first multiplies each number by 3 and then filters out the results that are not greater than 10. It will output [12, 15].

Conclusion

The map() function in JavaScript is a robust tool for array transformation, enabling effective and efficient data handling. Used standalone or combined with other array methods, it offers versatile solutions for various data manipulation needs. Embrace map() in your projects to simplify array transformations and maintain clean, readable code.