CODEWITHSUNDEEP
javascriptreduxfunction-composition
Amit Erandole
Amit Erandole

Reputation: 12281

Please explain how the compose function in redux works

The compose function in Redux is really simple for the most part and I understand how to use it. 

export default function compose(...funcs) {
  if (funcs.length === 0) {
    return arg => arg
  }

  if (funcs.length === 1) {
    return funcs[0]
  }

  return funcs.reduce((a, b) => (...args) => a(b(...args)))
}

However, this one part of the last bit seems really obscure to me:

funcs.reduce((a, b) => (...args) => a(b(...args)))

What is the ...args part? I understand these are rest parameters but what is it evaluating to? Where is it coming from?

Upvotes: 0

Views: 750

Answers (1)

Niraj
Niraj

Reputation: 496

Compose is just allowing you to write 

compose(func1, func2, func3, func4)

instead of

func1(func2(func3(func4))))

In case of 

funcs.reduce((a, b) => (...args) => a(b(...args)))

.reduce is a function of array, you can read about Array Reduce function

It is returning 

(...args) => a(b(...args);

and giving you an option to pass some parameters to the nested functions.

for example: It is allowing you to write something like this:

 nestedFunc = compose(func1, func2, func3);

 nestedFunc({key: value})

which will result in 

func1(func2(func3({key: value})))

Read more about compose function

Upvotes: 1

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