CODEWITHSUNDEEP
javascriptreactjs
user9623401
user9623401

Reputation:

when is setState() invoked?

I'm new to React, just a question on setState(), below is a component:

...
handleEvent = (event) => {
 this.setState({greeting: 'Hello'});
 }

render() {
   ...
   <button onClick={ this.handleEvent }>Click</button>

I was told React apply changes asynchronously, my questions are:

Q1- does it mean that the component's state will not be updated before the handleEvent function finishes? and the state will only get updated some time after handleEvent function finishes?

Q2- By the meaning of asynchronously, it means changes could happen any time, so does it still means that state changes still possible apply before handleEvent function finishes? it just a matter of probability, which is most of times state changes apply after callback function finishes?

Upvotes: 1

Views: 53

Answers (1)

Jonas Wilms
Jonas Wilms

Reputation: 138267

Q1 - Yes.

Q2 - No. JS functions have a run to completion guarantee. In other words: As long as the handleEvent function runs, no other function will run. The state update will definetly happen afterwards.

Upvotes: 4

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