A callback is a function that is passed to an another function. A callback may or may not be executed asynchronously. For example;
function two()
{
return 2;
}
function x(y)
{
//execute y
return y();
}
console.log(x(two)); //2
{
return 2;
}
function x(y)
{
//execute y
return y();
}
console.log(x(two)); //2
Here two() is a function. We are passing it as callback to function x(). Function x() may or may not execute it asynchronously. Here callback is executed asynchronously.
A Promise is a object which takes a callback and executes it asynchronously. For example;
function two()
{
return 2;
}
function error(e)
{
console.log(e);
}
var promise = new Promise(function(callback, e){
console.log(callback());
});
promise.then(two, error);
{
return 2;
}
function error(e)
{
console.log(e);
}
var promise = new Promise(function(callback, e){
console.log(callback());
});
promise.then(two, error);
Here we passed two() as callback to promise’s then() function which is indeed executed asynchronously.
Leave a Reply