map method

The map method in JavaScript is an array method used to create a new array by applying a provided function to each element in the original array. It’s particularly useful when you need to transform or process each element and return a new array with the results, leaving the original array unchanged.

Syntax:

const newArray = array.map(function(element, index, array) {
  // Return transformed element here
}, thisArg);

element: The current element being processed in the array.

index (optional): The index of the current element being processed.

array (optional): The array map was called upon.

thisArg (optional): A value to use as this when executing the callback function.

Characteristics of map

1. Returns a New Array: The map method returns a new array containing the results of applying the provided function to each element of the original array.

2. Original Array Unchanged: The original array remains unchanged after the map operation.

3. Transforms Each Element: The function provided to map transforms each element in the array, and the result of this transformation is stored in the new array.

4. Iterates Over Every Element: The function passed to map is called for every element in the array, even if the element is undefined, null, or an empty slot.

5. Chaining: Since map returns a new array, you can chain other array methods like filter, reduce, etc., on the result.

Example:

const numbers = [1, 2, 3, 4];
const updatedNumbers = numbers.map(num => num * 5);

console.log(updatedNumbers); // Output: [5, 10, 15, 20]
console.log(numbers); // Output: [1, 2, 3, 4] (original array is unchanged)

Extracting Specific Properties:

const users = [
    {name: 'John', age: 39},
    {name: 'Tom', age: 38},
    {name: 'Mathew', age: 35}
];

const names = users.map(user => user.name);

console.log(names); // Output: ['John', 'Tom', 'Mathew']

map method – Interview Questions

map method – Objective Questions (MCQs)