How does setState work?

Question

React

I can’t find such information on the work of setState: are the fields of the state object inside setState updated asynchronously with each other or not? And if you cause a change, for example, of the same field of the counter counter to +1 within one setState, will they be incremented asynchronously?

Answer 1

Duplicate properties in an object literal override each other. The value of the latter gets into the created object. Example.
So the object returned by the function call is:

prevState => ({
  counter: prevState.counter + 1,
  counter: prevState.counter + 1,
})

with , will be generated as:prevState.counter === 0

{
  counter: 0 + 1,
  counter: 0 + 1,  // результат этого выражения попадет в созданный объект
}

and the output will be an object: It will be mixed into the new state object.