JS: Concurrancy and Event Loop

Event Loop

JavaScript has a concurrency model based on an "event loop". The event loop got its name because of how it's usually implemented, which usually resembles:

while (queue.waitForMessage()) {
  queue.processNextMessage();
}

queue.waitForMessage() waits synchronously for a message to arrive if there is none currently.

1. Each message is processed completely before any other message is processed.
2. setTimeout message: a minimum time and not a guaranteed time.
3. A web worker or a cross-origin iframe has its own stack, heap, and message queue. 
4. A very interesting property of the event loop model is that JavaScript, unlike a lot of other languages, never blocks. Handling I/O is typically performed via events and callbacks

Node JS Architecture – Single Threaded Event Loop

• The first basic thesis of node.js is that I/O is expensive.
• The second basic thesis is that thread-per-connection is memory-expensive.
• There is no way of making code run in parallel within a single request. However, all I/O is evented and asynchronous.
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