A custom callback function can be created by using the callback keyword as the last parameter. It can then be invoked by calling the callback() function at the end of the function. The typeof operator is optionally used to check if the argument passed is actually a function.
Non anonymous callback function:
A callback function is not always required to be defined as an anonymous function. It may be defined elsewhere and this function can be used later as a callback. The parentheses are not used when passing the callback function.
Arguments in a callback function:
The callback function can also have its own arguments and the values can be passed while invoking the callback function in the body of the calling function.
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