How to queue a (macro)task in the JavaScript task queue?

Question

What is the most straight-forward and direct way to queue a task in the browser event loop, using JavaScript?

Things that don't work:

• window.setImmediate(func): Non-standard.
• window.setTimeout(func, 0)/window.setInterval(func, 0): Browsers throttle timers to ≥ 4ms.
• new Promise(r => r()).then(func): That queues a microtask, not a task.

Answer 1

MessagePort.postMessage does just that.

onmessage = e => handleMessage;
postMessage("","*");

You can even use a MessageChannel if you want a less intrusive mean:

const channel = new MessageChannel();
channel.port1.onmessage = handleMessage;
channel.port2.postMessage('');

This is currently the only API that does queue a task synchronously, all others implying at least some in parallel execution.

Maybe one day we will have a scheduler.postTask method, which would even allow us to specify some priority for our tasks, but that's for the future only...