CallBack function execution in javascript?

Question

function nestedFunction() {
  console.log('nested function');
}
function firstFunction(cb) {
  cb(nestedFunction());
}

function resetRouter() {
  setTimeout(() => {
    console.log('hello');
    firstFunction(() => {
      console.log('inside oye oyr');
    });
  }, 1000);
}

resetRouter();

This is my function . In this first reset Router is executed. Inside resetRouter after 1 second my first function is getting executed. First function takes a callback function as a param . Till here the things are clearer to me. But when the firstFunction is getting called it recieves a cb as a param , we are executing the callBackfunction and inside that callback function we are passing the nested function . So here first our nested function gets executed then the cb(callBack gets executed). So how is this being executed. Please someone explain its execution in a more clearer and easy way.

Joseph · Accepted Answer · 2020-06-18 19:59:20Z

1

function firstFunction(cb) {
  cb(nestedFunction());
}

You're not passing nestedFunction. You're passing the value resulting from invoking nestedFunction (see the () after it). If you just want to pass a reference to nestedFunction into cb, just pass the name.

function firstFunction(cb) {
  cb(nestedFunction);
}

answered Jun 18, 2020 at 19:59

Joseph

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Comments

Angshu31 · Accepted Answer · 2020-06-19 09:15:09Z

1

This is what happens:

1: resetRouter gets called.
2: In 1 second:
   a. resetRouter logs "hello" in the console.
   b. call `firstFunction` with the argment - () => console.log("inside oye oyr")
      note: the callback function doesn't get executed in this step.

   c. nestedFunction gets called.
   d. nestedFunction logs "nested function"
   e. the callback in `b` gets called with one argument - undefined
   f. finally, `b` logs "inside oye oyr" in the console.

Output:

hello           // from resetRouter
nested function // from nestedFunction
inside oye oyr  // from firstFunction callback.

edited Jun 19, 2020 at 9:15

answered Jun 18, 2020 at 20:15

Angshu31

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