Let's take this example:

function foo(callback){
        callback();
        baz();
  }

  function baz() {
        console.log('Hello from baz');  
   }

   foo(baz);

It looks like they are doing the same task. Or callback and calling a function inside another function are the same thing?

CodePudding user response：

Except you aren't using the callback the way callbacks are supposed to be used. Callbacks are supposed to get the interim results from a previous function. Here's an example

function add (a, b) {
  return a   b;
}

function subtract (a, b) {
  return a - b;
}

This is the callback

function doLater (val) {
  if (val > 0) {
    console.log("positive");
  } else if (val ==) {
    console.log("zero");
  } else console.log ("negative");
}

function doOp (a, b, mathOp, callback) {
  var res = mathOp(a,b);
  callback(res);
}

doOp (2,3, add, doLater);

vs.

doOp (2,3,subtract, doLater);

CodePudding user response：

Basically, they are doing the same, but callbacks are very useful because you can call the same function with many different callbacks. That makes your foo function more reusable.

CodePudding user response：

In your example, both approaches will do the same.

However, you can pass function as parameters, that are not in the functions scope. E.g.

function foo(callbackFn){
    callbackFn();
    // function test is undefined here, since it was declared in another scope 
}

function bar(){
    // test is only available in bar's scope
    function test(){
        console.log("test");
    }
    foo(bar);
}