Determine whether a method is synchronous or asynchronous

Question

In node.js, is it possible to determine (using a function) whether a method is synchronous or asynchronous?

I\'d like to write a function that does the following:

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Answer 1

You don't necessarily know. A function could even be randomly synchronous or asynchronous.

For example, a function that takes another function could execute that function immediately, or it could schedule to execute it at a later time using setImmediate or nextTick. The function could even randomly choose to call its passed function synchronously or asynchronous, such as:

console.log('Start')

function maybeSynchOrAsync(fun) {

  var rand = Math.floor((Math.random() * 2))

  if (rand == 0) {
    console.log('Executing passed function synchronously')
    fun()
    console.log('Done.')
  } else {
    console.log('Executing passed function asynchronously via setImmediate')
    setImmediate(fun)
    console.log('Done.')
  }
}

maybeSynchOrAsync(function () { console.log('The passed function has executed.') });

Further, technically speaking, every function call is synchronous. If you call a function F, and F queues a callback function to be invoked later (using setTimeout or whatever mechanism), the original function F still has a synchronous return value (whether it's undefined, a promise, a thunk, or whatever).