javascript callback function

A callback function is a function passed into another function as an parameter, which is then invoked inside the outer function to complete some kind of action.




For example, we’ll write a function to check “user is eliglble for voting or not’ and pass a callback function as a parmeter.

function checkUserEligible(age, callback) // here callback receive a callback function
  {
     if (age >= 18)
     return callback(true);  // call callback function
     else
     return callback(false); // call callback function
  }

checkUserEligible(10, function(response) { // response comes from callback method  i.e true or false
  if (response === true)
  console.log("Eligible for voting");
  else
  console.log("Not Eligible for voting");
  // Output Not Eligible for voting
});

checkUserEligible(18, function(response) { // response comes from callback method  i.e true or false
  if (response === true)
  console.log("Eligible for voting");
  else
  console.log("Not Eligible for voting");
  // Output Eligible for voting
});

That’s it!. Please share your thoughts or suggestions in the comments below.

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