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Discussion on: `at` coming soon to ECMAScript

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edo78 profile image
Federico "Edo" Granata •

As described here it looks like .at() is barely useful to get the last item.
It's unclear if it can be used to loop through the array in reverse (eg. .at(-2)) because we could have an hard time figuring when we reach the first element and stop the loop.

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hisuwh profile image
Henry Ing-Simmons • • Edited 
for (let i = 1; i <= arr.length; i++) {
   console.log(arr.at(-i));
}
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edo78 profile image
Federico "Edo" Granata •

So we still have to use .length like in the classic way

for (let i = arr.length - 1 ; i >= 0; i--) {
  console.log(arr[i]);
}
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We just shifted the 1 from the length - 1 to the starting point
I'm struggling to see why we need .at()

BTW You should cange const to let in your example

 
hisuwh profile image
Henry Ing-Simmons •

You're right. I never use classic for loops anymore really. Too used to writing:

for (const item of arr) {
    // ...
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I agree though. Don't see the point of at. Equally if you wanted to iterate the loop in reverse:

for (const item of arr.slice().reverse()) {
   // ...
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laurieontech profile image
Laurie •

They gave you an example. You really don’t need to “correct” it.

 
edo78 profile image
Federico "Edo" Granata •

What's wrong with that? I saw that he already edited it because he used "0" as a starting point instead of "1", so I thought he would like a fix.

 
laurieontech profile image
Laurie •

Because they're not wrong. Let is just as valid as const from the perspective of the code. Without larger context it's just a preference. And you understood the example they were kind enough to provide just fine. Your response was to make yourself feel smart.

 
edo78 profile image
Federico "Edo" Granata •

Maybe I'm missing somethig as english isn't my first language but using const is wrong.
Javascript prevent you from reassigning a value to a const throwing an error TypeError: Assignment to constant variable.

I was the first one asking a question because I know that I don't know everything and I want to learn so I think others can appreciate if I reciprocate

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laurieontech profile image
Laurie •

Yes, you could loop through in reverse. The first non-element would return undefined.

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laurieontech profile image
Laurie •

Yes, if you have holes then you'll need to check relative to the length of your array.

 
edo78 profile image
Federico "Edo" Granata •

sure or you should do as suggested here dev.to/hisuwh/comment/1fcp7
I still miss the value of .at() beside being a sugar syntax to get the last item

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edo78 profile image
Federico "Edo" Granata •

Sadly you can't just check for an undefined element because array with "hole" like const arr = [1,,3,4]; can create a problem with that logic.