JavaScript Arrow Functionality

"Arrow" is the short-hand way of writing function. Before it, there was a much less-used operator in JS that would be handy way of writing "goes to" but that was not so popular as the arrow function.

function countdown(n) {
  while (n --> 0)  // "n goes to zero"
    alert(n);
}

By running this script, the 'n' value is decremented till it becomes zero. It is short hand nortation of the below code.

while( (n--)>0)

In the same way, the ==> function in JavaScript can be used to write the function.

// ES5
var selected = ArrayObj.filter(function (item) {
  return item.toUpperCase()
});

// ES6
var selected = ArrayObj.filter(item=>item.toUpperCase());

The syntax for arrow function is  

(param1, param2, …, paramN) => expression
// equivalent to: (param1, param2, …, paramN) => { return expression; }

()==>{return statement;} // with no parameter

This way of notation is very useful for writing functions in making filter,s maps, or performing any operation in array object along with doing small manipulations.

// An empty arrow function returns undefined
let empty = () => {};

(() => 'foobar')();
// Returns "foobar"


var compareVar= a => a > 15 ? 15 : a;
compareVar(16); // 15
compareVar(10); // 10

let max = (a, b) => a > b ? a : b;

// Easy array filtering, mapping, ...

var arr = [5, 6, 13, 0, 1, 18, 23];

var sum = arr.reduce((a, b) => a + b);
// 66

var even = arr.filter(v => v % 2 == 0);
// [6, 0, 18]

var double = arr.map(v => v * 2);
// [10, 12, 26, 0, 2, 36, 46]

Next time, for writting an inline function, the arrow operator can be used.