在反应中访问组件 state

Question

I am interested in understanding why setting a components state (setState()) is slow to update ie I may read an old value after the fact that I called setState(). Additionally i am interested in knowing if reading the component state also incurs a penalty to know if I should minimize the number of reads/writes to component state. I tried looking for the documentation at the react website but no dice. Thanks

Answer 1

setState() is asynchronous, so you won't get the new value in the same function where you update it

Answer 2

React batch multiple setState() calls into a single update for performance. Because this.props and this.state may be updated asynchronously, you should not rely on their values for calculating the next state. https://reactjs.org/docs/state-and-lifecycle.html#state-updates-may-be-asynchronous