Spread, rest parameters

CSS

pre {
  padding:16px;
  border-bottom: 1px solid lightgray;
}

JavaScript

let log = (data) => document.body.innerHTML += `<pre>${JSON.stringify(data, null, '  ')}</pre>`

function test() {
	log(arguments);
}

let test2 = () => { log(arguments) };

try {

let m = [1,2];
let m2 = [3,4];
log ([...m, ...m2]);

test();
test(m);
test(m2);
test(...m);

test2();
test2(m);
test2(m2);
test2(...m);



} catch (e) {
  log(e.toString());
}