Sometimes reading comments about what microcontrollers aren't able to do in 2020 looks like cargo cult of people lacking the experience of how it was like to code with 640 KB.

  function increment() {
    var out = []

    for (let i of [1,2,3,4,5]) {
      out.push(i + 1)
    }

    return out
  }

  const increment = () => [1,2,3,4,5].map(i => i + 1)

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

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

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';

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

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

I will concede that I failed to write a function definition, thanks for catching that. I guess I unintentionally refactored the outer function away because development brain took over? Sloppy on my part, regardless.

The point was that modern JS is more convenient to use: Const/let, arrows, classes, proxies, async/await, generators, destructuring, default/rest/spread parameters, etc.

Even if you discard const/let/arrows as merely syntactic improvements (which they are not), you should not ignore the others - unless of course they are all syntactic improvements with added features at which point "syntax" lost its "meaning".

In fact, your example suffers from the same problem: It sorts in descending order (20,10,2,1) instead of ascending (1,2,10,20).

Telling JS to use a TypedArray [Int8,...,BigInt64] instead can solve this without remembering and providing your own comparator:

    Float64Array.from([1,2,10,20]).sort(); //[1,2,10,20]

I.e. due to the lack of typing this will fly just fine:

const calculateInterestingNumber = () <calculations goes here>;

let twiceAsInterestingNumber = 2 * calculateInterestingNumber; // (ooops, missing parenthesis)

... until runtime.

This was just the silliest contrived example.

In practice this - as you are fixing someone else's code and misplace/forget a set of parenthesis - ends up taking 30 minutes to figure out.

I highlight that. In fact, Rust is another kid on the block that is very promising for embedding.

In the other hand, sorry but I simply don't get why JS for interactions on such highly constrained devices. Probably as you said, it's intended to do very simple things with less effort as possible.