What is the best or better implementation (using event handler) for this situation?

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Javascript

HTML5

DOM

, +

I want to set a click event for each list like this:

Example 0. use an inline event handlers**

HTML

<ul class="fruits">
    <li class="apple" onclick="show(apple)">Apple</li>
    <li class="orange" onclick="show(orange)">Orange</li>
    <li class="cherry" onclick="show(cherry)">Cherry</li>
    <li class="grape" onclick="show(grape)">Grape</li>
    <li class="kiwi" onclick="show(kiwi)">Kiwi</li>
</ul>

As shown above, Inline event handlers, is simple and intuitive, but it's deprecated. so I will use addEventListener method. However, the latter is many different ways to write and I don't know the best.

Here are a few writing ideas I've come up with.

What I have tried:

Example 1. Get the arguments value from class name or data-attribute.

JavaScript

const fruits = document.querySelectorAll(".fruits> li");

fruits.forEach((fruit) => {
  fruit.addEventListener("click", function () {
    // use the class name for matching with arguments. more option is data-attributes.
    const fruitName = fruit.className;
    show(fruitName);
  });
});

Example 2. Get the arguments value from a list in JS.

JavaScript

const fruitList = ["apple", "orange", "cherry", "grape", "kiwi"];

for (let fruit of fruitList) {
  let fruitElem = document.querySelector(`.fruits> li.${fruit}`);
  fruitElem.addEventListener("click", function(){
      show(fruit)
  });
}

Example 3. Get the arguments value from a list, more complex than EX2 for future management, in JS.

JavaScript

const fruitList = [
    {event: "click", key: "apple", func: show},
    {event: "click", key: "orange", func: show},
    {event: "click", key: "cherry", func: show},
    {event: "click", key: "grape", func: show},
    {event: "click", key: "kiwi", func: show},
]

for (let fruit of fruitList) {
    let fruitElem = document.querySelector(`.fruits> li.${fruit.key}`);
    fruitElem.addEventListener(fruit.event, function(){
        fruit.func(fruit.key);
    });
}

What I would like to ask is:

- Which is the best way to do this (EX0-3)?
- If it was you, how to implement this?

Please teach me.

Posted 30-Aug-21 19:43pm

Rin O

Updated 30-Aug-21 22:39pm

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Richard Deeming · Answer 1 · 2021-08-30T22:39:00

Solution 1

For something like this, the "best" approach is probably to use event delegation:
https://javascript.info/event-delegation[^]

JavaScript

document.querySelector('.fruits').addEventListener("click", function(event){
   const target = event.target.closest('li');
   show(target.className);
});

This has the advantage that it will also work for new elements added to the list via script after the event handler has been attached.

Posted 30-Aug-21 22:39pm

Richard Deeming

Comments

Rin O 31-Aug-21 11:04am

Thanks to give a solution.

Your solution is better than any example.
However, If I click on a padding area in ul, I catch the following error:
=> Cannot read property 'className' of null

So, I need to add a code to return if the clicked area isn't li element.

document.querySelector('.fruits').addEventListener("click", function(event){
   if (event.target.tagName != 'LI') return;  // add this line.
   const target = event.target.closest('li');
   show(target.className);
});

What do you think about this handling, and if it was you, how to solve this problem?

Richard Deeming 31-Aug-21 11:07am

That would break if you had sub-elements - for example:

<li class="apple">An item with <b>sub-elements</b></li>

If you click on the bold word, the target will be the <b> element.

Try this instead:

document.querySelector('.fruits').addEventListener("click", function(event){
   const target = event.target.closest('li');
   if (target) { show(target.className); }
});

Rin O 31-Aug-21 11:32am

It worked fine!! Thank you for letting me know.