带箭头的 React.js 事件 function 与没有任何 () function

Question

hello i am wondering why only normal functions like below works and arrow functions do not.

const Form = () =>{

    const [text, setText] = useState("");

    const handle=(e)=>{
       setText(e.target.value);
    }
    const alertText = (e) =>{
       console.log(text);
       alert(text);
    }

    return(
       <>
           <input onChange={handle}></input>
           <button onClick={alertText}>submit</button>
           <h1>{text}</h1>   
       </>
    )}

using arrow functions like <input onChange={()=>handle}> doesn't work at all and I have no idea what the difference between of them.

Answer 1

Well, that's because if you use an arrow function on the element you have to call it like this:

<input onChange={(e)=>handle(e)}>

Answer 2

component expects onChange as a function, that function will be called when the user changes the value of the input.

NOTE: It's syntactically correct but the handle function will not execute.

When you do

<input onChange={handle}></input>
// it's equivalent to
<input onChange={(e)=>{ setText(e.target.value); }}></input>

But when you do

<input onChange={()=>handle}></input>
// it's equivalent to
<input onChange={(e) => ()=>{ setText(e.target.value);}}></input>

Answer 3

You can do:

 <input onChange={(e)=>handle(e)}>

You are not passing the event into the handle function

Answer 4

 <input onChange={()=>handle}> 

In above case onChange is assigned a function which has a single statement handle inside it. So onclick the statement handle is run. nothing happens.

 <input onChange={()=>handle()}> 

In above case onChange is assigned a function which has a single statement handle() inside it. So onclick handle is executed.

<input onChange={handle}>

In above case onChange is assigned handle function. So onclick handle is executed.