A reducer (also called a reducing function) is a function that accepts
an accumulation and a value and returns a new accumulation. They are used
to reduce a collection of values down to a single value
Reducers are not unique to Redux—they are a fundamental concept in
functional programming. Even most non-functional languages, like
JavaScript, have a built-in API for reducing. In JavaScript, it's
Array.prototype.reduce().
In Redux, the accumulated value is the state object, and the values being
accumulated are actions. Reducers calculate a new state given the previous
state and an action. They must be pure functions—functions that return
the exact same output for given inputs. They should also be free of
side-effects. This is what enables exciting features like hot reloading and
time travel.
Reducers are the most important concept in Redux.
Do not put API calls into reducers.
Type Parameters
S = any
The type of state consumed and produced by this reducer.
A reducer (also called a reducing function) is a function that accepts an accumulation and a value and returns a new accumulation. They are used to reduce a collection of values down to a single value
Reducers are not unique to Redux—they are a fundamental concept in functional programming. Even most non-functional languages, like JavaScript, have a built-in API for reducing. In JavaScript, it's
Array.prototype.reduce().In Redux, the accumulated value is the state object, and the values being accumulated are actions. Reducers calculate a new state given the previous state and an action. They must be pure functions—functions that return the exact same output for given inputs. They should also be free of side-effects. This is what enables exciting features like hot reloading and time travel.
Reducers are the most important concept in Redux.
Do not put API calls into reducers.