Currying is an advanced technique of working with functions. It’s used not only in JavaScript but in other languages as well.
Currying is a transformation of functions that translates a function from callable as f(a, b, c) into callable as f(a)(b)(c).
Currying doesn’t call a function. It just transforms it.
Curried functions are higher-order functions that allow us to create specialized versions of original functions. Currying works thanks to closures, which retain the enclosing function scopes after they have returned.
Summary
Currying is a transform that makes f(a,b,c) callable as f(a)(b)(c). JavaScript implementations usually both keep the function callable normally and return the partial if the arguments count is not enough. Currying allows us to easily get partials.
A Callback function is a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of routine or action.
Here is a quick example:
The above example is the synchronous callback, as it is executed immediately.
Note, however, that callbacks are often used to continue code execution after an asynchronous operation has completed — these are called asynchronous callbacks. A good example is the callback functions executed inside a .then() block chained onto the end of a promise after that promise fulfills or rejects. This structure is used in many modern web APIs, such as fetch().
