I believe the two articles in question are just using different terminology.
In article 1:
An event loop has multiple task sources which guarantees execution order within that source...
In article 2
the event loop can have multiple task queues... tasks must be processed in insertion order in every queue.
To answer my own question about observing different queues, I think it's as simple as this:
function foo() {
console.log('Start of queue');
bar();
Promise.resolve().then(function() {
console.log('Promise resolved');
});
console.log('End of queue');
}
function bar() {
setTimeout(function() {
console.log('Start of next queue');
console.log('End of next queue');
}, 0);
}
foo();
//-> Start of queue
//-> End of queue
//-> Promise resolved
//-> Start of next queue
//-> End of next queue
The first task queue (or task source) is foo(). foo() calls bar(), and bar() calls a setTimeout() which sets up a new task queue (or task source). The way we can observe each task queue is to resolve a Promise. The Promise callback is inserted into the micro queue. All micro queue tasks are executed at the end of every task queue (or task source). Because we see Promise resolved between the End of queue and Start of next queue console logs, we can conclude that that we're observing different event queues.
