Add a Key to a React Fragment

When working with CSS Grid, nesting elements can break the layout.

1const gridData = data.map(
2  ({ id, firstName, lastName, team }) => {
3    return (
4      <>
5        <span>{firstName}</span>
6        <span>{lastName}</span>
7        <span>{team}</span>
8      </>
9    )
10  },
11)
12

This function uses the <> fragment shorthand to return three <span> elements. With some CSS magic, it works great! But React will say that every element created in a loop needs a key.

The easy way to add the key is to add it to the parent, but since <key={id}> is an obvious syntax error, what can be done? Wrapping it in a <div key={id} solves the key issue but breaks the layout.

1const gridData = data.map(
2  ({ id, firstName, lastName, team }) => {
3    return (
4      <div key={id}>
5        <span>{firstName}</span>
6        <span>{lastName}</span>
7        <span>{team}</span>
8      </div>
9    )
10  },
11)
12

One solution is to add keys directly to each child. Since keys need to be unique, you can tag each one with the field name it corresponds to. This is a perfectly valid solution

const gridData = data.map(
  ({ id, firstName, lastName, team }) => {
    return (
      <>
        <span key={`${id}:firstName`}>
          {player.firstName}
        </span>
        <span key={`${id}:lastName`}>
          {player.lastName}
        </span>
        <span key={`${id}:team`}>
          {player.team}
        </span>
      </>
    )
  },
)

But – as it turns out, the long-form React.Fragment has no problem accepting propsThe only props that are valid for a React.Fragment are key and children, as noted in the source code here, and we can just key on that instead.

const gridData = data.map(
  ({ id, firstName, lastName, team }) => {
    return (
      <React.Fragment key={id}>
        <span>{firstName}</span>
        <span>{lastName}</span>
        <span>{team}</span>
      </React.Fragment>
    )
  },
)

Add a Key to a React Fragment

Hi, I'm Jacob