CODEWITHSUNDEEP
reduxreact-redux
stackjlei
stackjlei

Reputation: 10035

What is the philosophy behind Redux completely replacing the state instead of mutating it each time?

I heard that it's better to do testing this way but I don't understand why. What purpose does it serve to build a new state each time something changes rather than mutating what is already there? Is it faster?

Upvotes: 0

Views: 37

Answers (2)

CodinCat
CodinCat

Reputation: 15914

No it's not faster. Mutating the state directly is usually faster.

Returning a new state makes reducers easier to test and predictable (because there is no side effect), also we can prevent some unexpected behaviors from happening. For example If you are using PureComponent and you mutate state directly, you component may not update as you expected, because PureComponent use === to compare props.

Consider the code below, we are trying to render a list:

// current state
const list = ['foo', 'bar']

// we mutate the state directly
list[1] = 'hihi'

// in shouldComponentUpdate of a PureComponent
props.list === nextProps.list // true

In this case the component will not be aware of the update.

In addition to PureComponent, there are some optimizations in react-redux rely on this convention.

Upvotes: 1

Michael Peyper
Michael Peyper

Reputation: 6944

Take a read of the Redux docs on the issue, but basically it makes each update much more preditable, which makes everything from testing to rendering simpler.

Upvotes: 0

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