JavaScript does have concurrency! Try the following:

    Promise.all([new Promise(t => setTimeout(t, 3000)), new Promise(t => setTimeout(t, 3000))]).then(() => console.log('done'))

You'll notice it prints `done` after 3 seconds, not after 6.

It just happened to be executed one by one but the VM handles the switching for us.

What you're talking about is parallelism, which JavaScript indeed does lack and you'd use cluster or workers for that. That's when things happen at the same time, outsourced to different cores. This is what JavaScript cannot do (yet?).