Dave Bernhard

Web Developer

📚 Reading: The Riddle-Master of Hed by Patricia A. McKillip

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Mapping a list in React: altering the last element


🔥 Bonfire|First lit on March 10, 2021
3 min read
Table of contentsCode that does thingsLet's assume an array of Power Rangers

It is a truth universally acknowledged, that a coding man (woman, other) in possession of good arrays, must be in want of JSX.

Poor Jane. Her insightful, sensitive, entertaining work has been co-opted by mysoginy, by people wanting to give Colin Firth something to do, and now by yet another React tutorial. She'd probably have been into Vue; maybe she'd have considered rolling in the muddy frontend obscene and opted for Lisp or Haskell. Never mind.

Code that does things

This is pretty simple so I'm not going to bang on about Austen any longer. This is mostly a reminder to myself, because although it's not overly complicated, it did trip me up for a few minutes at work, and I wasn't totally sure what to search for to unblock myself. Besides, I do hope, intrepid blog-burrower (that's you, my furry little reader), that it is also useful to you.

Let's assume an array of Power Rangers

PR fans (not Public Relations. They don't shout "it's morphing time!" do they?) will notice that the names belong to the first lot of Power Rangers and that I've omitted the Green guy. He later became the White Ranger, which I was never comfortable with. How could I be? Way too big for his boots...

Here's how we could list out our heroes, putting an <hr /> (horizontal rule) after each but the last. First, we remember that the second argument of JavaScript's .map() array function is an index. Then, we use it:

const powerRangers = [
  {
    color: 'Red',
    name: 'Jason Lee Scott'
  },
  {
    color: 'Yellow',
    name: 'Trini Kwan'
  },
  {
    color: 'Black',
    name: 'Zack Taylor'
  },
  {
    color: 'Pink',
    name: 'Kimberly Hart'
  },
  {
    color: 'Blue',
    name: 'Billy Cranston'
  }
]

const listOfRangers = () =>  (
  <ol>
    {powerRangers.map(({ color, name }, index) => (
      <>
        <li key={index}>
            {name} was the {color} Ranger
        </li>
        {index === powerRangers.length - 1 ? null : <hr />}
      </>
    ))}
  </ol>
)

That handy <> tag is the same as React.Fragment. Since we're rendering an li and an hr as siblings (for all but the last Ranger), we need to wrap them in a parent element. You could opt for a div if you were going to use it for something. Remember to move the key attribute to it if you do.

Of course, it doesn't need to be the last element of the array. Once you have the current index, you can do anything your bloody, pumping heart desires. index === 0 ? <hr /> : null would add an hr after the first element only, for instance. Anyway, happy mapping!