为什么在ruby循环中var起作用但const不起作用？

Question

I'm trying to toggle each untagged task. This works,

<% @untagged.each do |task| %> 
    var task_id = <%= task.id %>;
    $(`#${task_id}`).fadeToggle();
<% end %>

But, quite curiously this doesn't.

<% @untagged.each do |task| %> 
    const task_id = <%= task.id %>;
    $(`#${task_id}`).fadeToggle();
<% end %>

From my understanding, every loop creates a new block. The constant declaration will be nested in each of these blocks, thus there wouldn't be any redeclarations. So why is the second example not working?

Thank you in advance!

Answer 1

What does your code do?

For every element in @untagged , it generates the following lines of code:

const task_id = FOO;
$(`#${task_id}`).fadeToggle();

with FOO replaced by the element's ID. Let's assume, @untagged looks like this: [<#Task @id = 23>, <#Task @id = 24>] , then the generated code will look like this:

const task_id = 23;
$(`#${task_id}`).fadeToggle();
const task_id = 42;
$(`#${task_id}`).fadeToggle();

In ECMAScript, const ants can only be declared and assigned once, ergo, you get a static error. That's just how constants work in ECMAScript and doesn't really have anything to do with ruby-on-rails at all.