The tool exits the event loop when there are no more callbacks to perform. It simply enters the event loop after executing the input script. In Node js, there is no such start-the-event-loop call.
Typically behavior is defined through callbacks at the beginning of a script and at the end starts a server through a blocking call like EventMachine::run(). In other systems, there is always a blocking call to start the event-loop. It presents an event loop as a runtime construct instead of a library. Node.js is similar in design to and influenced by, systems like Ruby's Event Machine or Python's Twisted. Because nothing blocks, scalable systems are very reasonable to develop in Node. Almost no function in the app directly performs I/O, so the process never blocks. Furthermore, users of Nodejs are free from worries of dead-locking the process, since there are no locks. Thread-based networking is relatively inefficient and very difficult to use. This is in contrast to today's more common concurrency model where OS threads are employed. Upon each connection, the callback is fired, but if there is no work to be done, Node 64 bit will sleep. In the following "hello world" example, many connections can be handled concurrently. As an asynchronous event-driven JavaScript runtime, Node is designed to build scalable network applications.
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