TypeError: Cannot read property 'target' of undefined - React JS

user_15650029 0
Viewed 1195

So I'm trying to read the value of something that triggered the event, in my case its Select tag but when I change the tag its giving me an error saying TypeError: Cannot read property 'target' of undefined. I think it means event or target in undefined, My code is like this

function RandomScreen() {
  
  function handleChange(event) {
   ChangeSomeOtherState(event.target.value)
}

  return (
    <select onChange={() => handleChange()}>
            {StateWhichIsArray.map(String => {
                return (
                <option value={String} key={String} >{String}</option>
                )
            })}
        </select>
 )
}
reactjs javascript
3 Answers

You are not passing any value to callback function , can do it like this


  <select onChange={(e) => handleChange(e)}>

Or


  <select onChange={handleChange}>

You can refer to this codesandbox to do it right way

Edit misty-forest-3gio1

user_76818390

Remove expression to make the function get called with the calling event

<element onChange={eventHandler}>

Use expression callback when you want to pass any data to handler, Note this, when you do this way, you are creating a fn each time event get triggered which get heavy when you attach this to events like scroll or keypress or drag so be cautious when you do this

<element onChange={(yourData) => eventHandler(yourData)}>

So In your case it will look like this

return (
    <select onChange={handleChange}>
            {StateWhichIsArray.map(String => {
                return (
                <option value={String} key={String} >{String}</option>
                )
            })}
        </select>
 )
user_73583080

The answer was answered by Gouthman ans Satyam, but i will try to explain what happened there with more details because I've seen that is a recurrent error in a lot of developers.

  1. The select selector executes the arrow function that you define implicitly.
  2. The arrow function is who can take the event parameter but you are ignoring it and you are executing the handleChange function without pass the event object
  3. the handleChange function throws error because does not recognize the event object.
  4. Important thing: you are using an arrow function that calls another function passing the same value that gets by itself. It is redundant an unnnecessary, you could pass directly the handleChange function and make your code more concise and clear.
user_46125150
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