Waiting for a condition to be met in node.js

Question

Waiting for a condition to be met in node.js

I wrote a class cotaining the following CoffeScript code:

class SomeClass
  # ...lots of other code...

  runner: ->
    process.nextTick =>
      if @some_condition
        @do_something_async()
      @runner()

What it is supposed to do is to wait for @some_condition to be true. This basically works, however since it really quickly loops through all of this it causes heavy resource usage. How would I do this correctly?

node.js
coffeescript

Answer 1

Use events to decouple conditions and code that must run when those conditions are met.

Pattern is:

listen for an event and set a listener that would run when the event is fired

eventEmitter.on("myEvent", function () {
    console.log("myEvent just happened");
});

when something in your code can make your condition become true, check for it and fire an event accordingly:
```
doSomething();
something++;
if (something > max_something) {
    eventEmitter.emit("myEvent");
}
```

Answer 2

Instead of having a loop that waits for something to be true, just make a callback function and pass that in to the function that is running long and call the callback when the process is done.