Array map() Method In JavaScript

pradeep — Tue, 24 Aug 2021 13:00:20 +0000

The map() method in JavaScript creates an array by calling a specific function on each element present in the parent array. It is a non-mutating method. Generally map() method is used to iterate over an array and calling function on every element of array.

Syntax:

array.map(function(currentValue, index, arr), thisValue)

Parameters: This method accepts two parameters as mentioned above and described below:

function(currentValue, index, arr): It is required parameter and it runs on each element of array. It contains three parameters which are listed below:
- currentValue: It is required parameter and it holds the value of current element.
- index: It is optional parameter and it holds the index of current element.
- arr: It is optional parameter and it holds the array.
thisValue: It is optional parameter and used to hold the value of passed to the function.

Return Value: It returns a new array and elements of arrays are result of callback function.

Below examples illustrate the use of array map() method in JavaScript:
Example 1: This example use array map() method and return the square of array element.

Output:

Example 2:

What are Rest parameters in JavaScript ?

pradeep — Tue, 24 Aug 2021 11:47:47 +0000

The rest parameter syntax allows a function to accept an indefinite number of arguments as an array, providing a way to represent variadic functions in JavaScript.

Now, What is variadic function ?

In mathematics and in computer programming, a variadic function is a function of indefinite arity, i.e., one which accepts a variable number of arguments. Support for variadic functions differs widely among programming languages.

What is Rest parameter

A function definition’s last parameter can be prefixed with “...” , which will cause all remaining (user supplied) parameters to be placed within a “standard” JavaScript array.. Only the last parameter in a function definition can be a rest parameter.

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