Map through an array of objects in js/react

Question

I need an array of alt strings. I can map the array with name strings, but can't get it to return the "alt". This is what I tried:

const data = [
  { name: "Apple", alt: "Fruit" },
  { name: "Banana", alt: "Fruit" },
  { name: "Potatoe", alt: "Vegetable" },
  { name: "Lentil", alt: "Legume" }];

  <span>
      {data.map(item => {
        return (
         <Button item={item.alt.toUpperCase()}>
         {item}
         </Button>
         );
       })}
  </span>

To get an array of namestrings, this worked:

  <span>
      {data.map(item => {
        return (
         <Button key={item.name} item={item.name.toUpperCase()}>
         {item}
         </Button>
         );
       })}
  </span>

This is the error: TypeError: Cannot read property 'toUpperCase' of undefined

you are returning {item} inside button, which is an object. Either return {item.name} or {item.alt} — shubham-gupta
– shubham-gupta, Commented Oct 18, 2019 at 5:17

Ankit Verma · Accepted Answer · 2019-10-18 05:40:22Z

2

I think you are trying to create a button please look below

The below code is modified to use key in map function as each of your record is unique and react keys are useful when working with dynamically created components or when your data are altered . Setting the key value will keep your components uniquely identified after the change and they also help in performance.You can read the below blog it explains well about using keys. https://programmingwithmosh.com/react/why-do-i-need-keys-in-react-lists/

 const data = [
      {id:1, name: "Apple", alt: "Fruit" },
      {id:2 ,name: "Banana", alt: "Fruit" },
      {id:3, name: "Potatoe", alt: "Vegetable" },
      {id:4, name: "Lentil", alt: "Legume" }
    ];
    function App() {
      return (
        <span>
          {data.map((item) => (
            <button key={item.id}>{item.alt.toUpperCase()}</button>
          ))}
        </span>
      );
    }

Use this link it is working here https://codesandbox.io/s/friendly-wave-t117u

edited Oct 18, 2019 at 5:40

answered Oct 18, 2019 at 5:16

Ankit Verma

946 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Mina Hawker Over a year ago

This is exactly what I need! But I still get this error: TypeError: Cannot read property 'toUpperCase' of undefined...

Ankit Verma Over a year ago

Hi Mina , Could you open the codesandbox and check.

SiddAjmera · Accepted Answer · 2019-10-18 05:15:09Z

0

Give this a try:

<span>{
  data.map(
    (item, index) => <button 
      alt={item.alt.toUpperCase()} 
      key={someKeyHere}>
        {item.alt.toUpperCase()}
      </button>)
}</span>

Here's a Working Sample StackBlitz for your ref.

answered Oct 18, 2019 at 5:15

SiddAjmera

39.6k7 gold badges77 silver badges113 bronze badges

Collectives™ on Stack Overflow

Map through an array of objects in js/react

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related