Functions

ES3

function sum(a, b) {
    return a + b
}

console.log(sum(5,6)) // 11

ES5

var sum = function(a, b) {
    return a + b
} 

console.log(sum(5,6)) // 11

ES6

const sum = (a, b) => a + b

console.log(sum(5,6)) // 11