To go maximum pedant, your `increment` is an array instead of a function which returns that array:

    var increment = function() {
        return [1,2,3,4,5].map(function(num) {
             return num + 1;
        });
    };

Moreover, modern JS is not merely convenient syntactic sugar over old JS. Let/const have different scopes, arrow functions have no bindable context.

You also now have classes, proxies, async/await, generators, destructuring, default/rest/spread parameters, ...

Add typing via jsdocs or TypeScript and - like the parent comment said - "it's really nice".

Often people mistake JS for a mere DOM manipulation language and think of

    document.getElementById('myDiv').innerHTML = 'Hello World';

instead of what it has become today.

I still hate it though for sorting arrays with only number types lexically:

    [1,2,10,20].sort(); //[1,10,2,20]