ARROW FUNCTIONS

New in ECMAScript 6 is the capability to define a function expression using the fat-arrow syntax. For the most part, arrow functions instantiate function objects that behave in the same manner as their formal function expression counterparts. Anywhere a function expression can be used, an arrow function can also be used:

let arrowSum = (a, b) => {
 return a + b;
};

let functionExpressionSum = function(a, b) {
 return a + b;
};

console.log(arrowSum(5, 8)); // 13 
console.log(functionExpressionSum(5, 8)); // 13 

Arrow functions are exceptionally useful in inline situations where they offer a more succinct syntax:

let ints = [1, 2, 3];

console.log(ints.map(function(i) { return i + 1; }));  // [2, 3, 4]
console.log(ints.map((i) => { return i + 1 }));        // [2, 3, 4]

Arrow functions do not require the parentheses if you only want to use a single parameter. If you want to have zero parameters, or more than one parameter, parentheses are required:

// Both are...