why we use => in javascript code example

Example 1: what is == in js

//== in Javascript means to check if a value is equal to another value, and it ignores types (quotes and things like that).
var stage = "begin";
if (stage == "begin") {
Bot.send ("Hello User!");
}
//Output:
//Hello User!

Example 2: () => javascript

var a = [
  "We're up all night 'til the sun",
  "We're up all night to get some",
  "We're up all night for good fun",
  "We're up all night to get lucky"
];

// Sans la syntaxe des fonctions fléchées 
var a2 = a.map(function (s) { return s.length });
// [31, 30, 31, 31]

// Avec, on a quelque chose de plus concis
var a3 = a.map( s => s.length);
// [31, 30, 31, 31]