[SOLVED] What happens with this use of the .map() function from Javascript/Typescript

Issue

I have a question about the .map() function which can be used on arrays.

The normal usage I know is like:

function myFunction(num) {
  return num * 2;
}

const numbers = [1, 2, 3, 4];
const newArr = numbers.map((element) => myFunction(element))

But in a code sample I saw the following usage:

const resultToRow = (r: MyProductsDto) => ({
  rowData: tableColumns.map(() => r),
});

In this example MyProductsDto is an Interface and tableColumns is an Array.
But what exactly does .map(() => r) ?

r is not a function but a Interface and why is the arrow function empty without any arguments?

Solution

As length as of tableColumns, there will be r[] in rowData

also it all the value of r[] will be same because it has one reference address.

r[0] === r[1] === [r2] === [r(n)]

map makes new array from original array each element will pass as argument but accept it (the argument that tossed by map) or not is not consideration of map it just makes new array with return value of given function.

Answered By – MINJA KIM

Answer Checked By – Clifford M. (BugsFixing Volunteer)

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