what is JS callback function?

A callback function is a function that is being called within another function. Meaning that when you call function one you pass your second function as an argument and it runs.

As you can see from the example below I have two functions X and Y. When I set my function y to accept an parameter, which in this case is another function. When I am calling function y I am passing function x as an argument.

Result in the console:

"I am called first" "I am called within the function"

function x(){ console.log("I am called within the function") }

function y(callback){ console.log("I am called first") callback() }

y(x);