How to turn a higher order "array function" into a higher order "regular function"?

Question

As I am learning react at the moment I came across this concept of event handler using "setState".

It is a little complicated for my understanding as 3 functions within each other. Case in point.

class Counter extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0
    };

this.increment = this.increment.bind(this)
    
increment(){
    this.setState(state => ({count: state.count+ 1}))
} 

//....some other code

This code works. I tried to understand the increment function a little further but I can't understand why the following code will not work:

increment(){
  this.setState(function anon(state){
    count: state.count+1
    })
}

What is wrong with this code?

@KrzysztofKrzeszewski also missing second pair of `{` and `}` for object/function body. — VLAZ, May 25 '21 at 07:19
Duplicate: [When should I use a return statement in ES6 arrow functions](https://stackoverflow.com/questions/28889450/when-should-i-use-a-return-statement-in-es6-arrow-functions) — Chris G, May 25 '21 at 07:26

adiga · Answer 1 · 2021-05-25T07:28:10.507

2

function anon(state) {
  count: state.count + 1
}

^ This function is neither creating an object, nor returning anything from the function. It is creating a label called count inside the function. So, it is not throwing a syntax error.

this.setState(state => ({ count: state.count+ 1 }))

^ This callback creates an object with count key and implicitly returns it. It is equivalent to the following code when you use a regular function

this.setState(function (state) => {
   return { count: state.count+ 1 }
})

edited May 25 '21 at 07:28

answered May 25 '21 at 07:19

adiga

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Yes, you are right. I forgot that arrow functions don't need the return syntax. – BitByBit May 25 '21 at 07:22
They do if they're inside curly brackets. Inside curly brackets the return must be explicit. – Andy May 25 '21 at 07:25

score 0 · Answer 2 · answered May 25 '21 at 07:24

0

The only missing part is return.

increment(){
  this.setState(function anon(state){
    return {count: state.count+1}
    })
}

answered May 25 '21 at 07:24

Charlie

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7
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How to turn a higher order "array function" into a higher order "regular function"?

2 Answers2