What is `emit` javascript function?

In node.js an event can be described simply as a string with a corresponding callback. An event can be "emitted" (or in other words, the corresponding callback be called) multiple times or you can choose to only listen for the first time it is emitted.

The on or addListener method (basically the subscription method) allows you to choose the event to watch for and the callback to be called. The emit method (the publish method), on the other hand, allows you to "emit" an event, which causes all callbacks registered to the event to 'fire', (get called).

reference: https://docs.nodejitsu.com/articles/getting-started/control-flow/what-are-event-emitters/ (This is an outdated link and doesn't work anymore)

Please look at line number 624 of the same file.

function emit (parser, event, data) {

  parser[event] && parser[event](data)

}

Short: Emit's job is to trigger named event(s) which in turn cause functions called listeners to be called.

Detailed: Node.js core API is built around an idiomatic asynchronous event-driven architecture in which certain kinds of objects (called "emitters") periodically emit named events that cause Function objects ("listeners") to be called.

All objects that emit events are instances of the EventEmitter class. These objects expose an eventEmitter.on() function that allows one or more functions to be attached to named events emitted by the object.

When the EventEmitter object emits an event, all of the functions attached to that specific event are called synchronously. Any values returned by the called listeners are ignored and will be discarded.

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