setState doesn’t update the state immediately

Your state needs some time to mutate, and since console.log(this.state.boardAddModalShow) executes before the state mutates, you get the previous value as output. So you need to write the console in the callback to the setState function

openAddBoardModal() {
  this.setState({ boardAddModalShow: true }, function () {

setState is asynchronous. It means you can’t call it on one line and assume the state has changed on the next.

According to React docs

setState() does not immediately mutate this.state but creates a
pending state transition. Accessing this.state after calling this
method can potentially return the existing value. There is no
guarantee of synchronous operation of calls to setState and calls may
be batched for performance gains.

Why would they make setState async

This is because setState alters the state and causes rerendering. This
can be an expensive operation and making it synchronous might leave
the browser unresponsive.

Thus the setState calls are asynchronous as well as batched for better
UI experience and performance.

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