If you're old like me (in my 40s) and got into JavaScript way before ES6 (2015) but didn't use the new syntax that came out post 2015 like arrow functions, then here's a preview of how to convert traditional functions to arrow functions - as an argument to a ES6 functions like find, map, filter and reduce.

const arr = [3, 5, 6, 8, 7];

console.log("=== Array ===");
console.log(arr);
console.log("");


// Find - will return 6

let es6_find_1 = arr.find(function(n)
{
    if (n % 2 === 0)
    {        
        return true;
    }

    return false;
});

let es6_find_2 = arr.find(n => n % 2 === 0);

console.log("=== Find ===");
console.log(es6_find_1);
console.log(es6_find_2);
console.log("");

// Map - will return [ 6, 10, 12, 16, 14 ]

let es6_map_1 = arr.map(function(n)
{
    return n * 2;
});

let es6_map_2 = arr.map(n => n * 2);

console.log("=== Map ===");
console.log(es6_map_1);
console.log(es6_map_2);
console.log("");

// Filter - will return [ 6, 8 ]

let es6_filter_1 = arr.filter(function(n)
{
    if (n % 2 === 0)
    {
        return true;
    }

    return false;
});

let es6_filter_2 = arr.filter(n => n % 2 === 0);

console.log("=== Filter ===");
console.log(es6_filter_1);
console.log(es6_filter_2);
console.log("");

// Reduce - will return 29

let es6_reduce_1 = arr.reduce(function(acc, cur)
{
    return acc + cur;    
});

let es6_reduce_2 = arr.reduce((acc, cur) => acc + cur);

console.log("=== Reduce ===");
console.log(es6_reduce_1);
console.log(es6_reduce_2);
console.log("");

Read : developer.mozilla.org/en-US/docs/Web/JavaSc..