TypeScript - reverse array

In this article, we would like to show how to reverse an array in TypeScript.

Quick solution:

const array: string[] = ['a', 'b', 'c'];
const reversedArray: string[] = array.reverse();

const display = (array: string[]): void => {
  console.log(array.join(' '));
};

display(array);         // c b a   <------  Pay attention or use copy !!!
display(reversedArray); // c b a

Note: be careful reversing array because reverse() method works on source array obcject. It is safe to call array.slice().reverse().

Safe reversion example

When we use array in another place of application it is safe to use source array copy.

const array: string[] = ['a', 'b', 'c'];
const reversedArray: string[] = array.slice().reverse();

const display = (array: string[]): void => {
  console.log(array.join(' '));
};

display(array);         // a b c
display(reversedArray); // c b a

Output:

a b c
c b a

Array map() method example

In 2009, ES5 introduced Array.prototype.map() method that lets us write quick reversion logic with an arrow function.

const array: string[] = ['a', 'b', 'c'];
const reversedArray: string[] = array.map(
  (item: string, index: number, array: string[]) => array[array.length - 1 - index]
);

const display = (array: string[]): void => {
  console.log(array.join(' '));
};

display(array);         // a b c
display(reversedArray); // c b a

Output:

a b c
c b a