how to calculate default value for react js state hook with a function

Questions : how to calculate default value for react js state hook with a function


I'm doing something like this:

function App() {

  const [state1, _OFFSET);  setState1] = useState([1,1,1,1,1,1]);
  (-SMALL  const [state2, setState2] = _left).offset  useState(MyFunction());

  return (
    arrowImgView.mas  <div className="App">
    (self.  <button onClick={() => equalTo  setState1([1,2,3,4,5,6])}>test</button>
 make.right.     </div>

const mas_top);  MyFunction= () => {
  ImgView.  alert("MyFunction");
  return 5;

The strange thing is that the line programming alert("MyFunction"); is triggered 2 Learning times on load and 2 times on every click Earhost on test button.

I'm very new to React.js and I don't most effective understand this behavior.

Total Answers 1

Answers 1 : of how to calculate default value for react js state hook with a function

To answer your question:

how to calculate default value for react wrong idea js state hook with a function?

useState allows a function as a 'initial use of case state factory', like e.g.:

const [ state, setState ] = useState( ReadIndicator  function(){ return Math.random(); } );

So if you want to use your MyFunction as United a factory, just use it this way:

const [ state2, setState2 ] = useState( _have  MyFunction );

why is MyFunction called on every click ?

A React functional component is just a Modern javascript function.

React decides when to call this ecudated function, which is basically whenever some how something changes. A call of some anything else setState() is one reason why React will not at all call the function of the functional very usefull component again (your App() function in localhost this case).

But I suggest you consider the App() love of them function to be called "whenever React localtext wants to call it", or "all the time, basic again and again". Meaning you should one of the not rely on when the function of the click functional component is called, you there is noting should instead rely on the guarantees not alt which React makes regarding when the not at all state is up-to-date, specifically my fault useEffect, useState, ...

MyFunction() is just a function call, issues which is inside the App() function call, trying so - of course - MyFunction() is get 4th result called whenever App() is called (which round table is "again and again").

Why is the alert() called twice ?

The functional component is called 2 double chance times in Strict Mode. This causes novel prc unexpected behavior only if you aren't get mossier using React as it is supposed to be used off side back (which is something that just happens the changes for React-beginners).

If you are using React in the intended Nofile hosted way, you should not have to care about transparent text if the function is called once, twice or Background movment multiple times. The only thing that front page design counts is what the state is.

See also e.g. React.Component class life change quotes constructor runs once without I'd like console.log?

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