.map .reduce .filter

whAT are the main work of these .map and .reduce and .filter

and why we use arrow (item) =>
can somebody explain .
the use of arrow

See the following challenges which discuss these methods.

See the following challenge related to arrow functions.

https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/es6/use-arrow-functions-to-write-concise-anonymous-functions

Arrow functions aren’t necessary for .map, .reduce, or .filter, nor the other way around. Arrow functions are (for most purposes) simply a more concise syntax for writing functions.

const ANIMAL_EMOJIS = ['🐢', '🐈', '🐒', 'πŸ¦„', 'πŸ•', '🐟'];

// the following two versions both return ['🐢', 'πŸ•']

// version 1:
function isDogEmoji(str) {
  return str === '🐢' || str === 'πŸ•';
}

ANIMAL_EMOJIS.filter(isDogEmoji);

//version 2:
ANIMAL_EMOJIS.filter(str => str === '🐢' || str === 'πŸ•');