5 ms·

Am I reading this correctly — it's an alias for arr[i] and str[i]? I know languages like Ruby have arr.at(i), but why?

by ezekg 5y ago

twoodfin 5y ago
A quick read suggests that it adds negative indexing from the end of the array.
- Pxtl 5y ago
  Imho that violates the principle of least astonishment - that "at" would have such different behavior from "[]" for negative numbers.
  - ZephyrBlu 5y ago
    That's the whole point of this though... Currently you can't use negative indexes, but this would make them usable.
    - Pxtl 5y ago
      Oh, I'd assumed main point was to provide a composable function.
  - deleted 5y ago
    [deleted]
pininja 5y ago
Accessing negative indexes currently returns undefined. This adds support for indexing from the end of an array with negative numbers.
- franciscop 5y ago
  This works, but not the way you'd think: const arr = []; arr[-1] = 'Hello world'; console.log(arr[-1]); // Hello world Instead of using the negative index, it stringifies the "-1" and uses it as the key of an object both when writing and reading. Thus, arr.length still remains 0
maweki 5y ago
It's a function object then.
nvartolomei 5y ago
Proposal hosted on GitHub explains the reasoning behind it https://github.com/tc39/proposal-relative-indexing-method https://github.com/tc39/proposal-relative-indexing-method
antris 5y ago
In addition to negative index support, a function is more easily composable e.g. converting a list of indices to a list of objects: `indices.map(myObjectArr.at)` I've lost count on how many times I've wrote this function manually.
- bidirectional 5y ago
  > `indices.map(myObjectArr.at)` That works in this case, but eta-reduction is not generally safe in Javascript due to the variadic nature of many functions, so I wouldn't recommend it in production code. For example `indices.forEach(console.log)` does not work as one would expect.
  - antris 5y ago
    Better a function that works in some cases than not having a function at all. Also, by using TypeScript definitions you pretty much always know what's coming in and going out and VS Code will yell at you if you're trying to do something stupid.
    - e1g 5y ago
      A function that works in some cases will be a nightmare to debug. The pattern of `indices.map(myObjectArr.at)` is discouraged in JS because it often fails in unexpected ways. For example - ["1","2"].map(parseFloat) // works as expected ["1","2"].map(parseInt) // nope
      - antris 5y ago
        I've learned ages ago that parseInt cannot be used like this, so it's not a problem for me, but I thought linters already take care of this case? Also I wasn't talking about using parseInt, a broken function like this so I'm not sure what the quirks of old, widely known bad parts of Javascript have to do with using functions as arguments, which is one of the most powerful features of the language.
        5y ago

Am I reading this correctly — it's an alias for arr[i] and str[i]? I know languages like Ruby have arr.at(i), but why?

by ezekg 5y ago

Am I reading this correctly — it's an alias for arr[i] and str[i]? I know languages like Ruby have arr.at(i), but why?

twoodfin 5y ago

A quick read suggests that it adds negative indexing from the end of the array.

Pxtl 5y ago
Imho that violates the principle of least astonishment - that "at" would have such different behavior from "[]" for negative numbers.
- ZephyrBlu 5y ago
  That's the whole point of this though... Currently you can't use negative indexes, but this would make them usable.
  - Pxtl 5y ago
    Oh, I'd assumed main point was to provide a composable function.
- deleted 5y ago
  [deleted]

pininja 5y ago

Accessing negative indexes currently returns undefined. This adds support for indexing from the end of an array with negative numbers.

franciscop 5y ago
This works, but not the way you'd think: const arr = []; arr[-1] = 'Hello world'; console.log(arr[-1]); // Hello world Instead of using the negative index, it stringifies the "-1" and uses it as the key of an object both when writing and reading. Thus, arr.length still remains 0

maweki 5y ago

It's a function object then.

nvartolomei 5y ago

Proposal hosted on GitHub explains the reasoning behind it https://github.com/tc39/proposal-relative-indexing-method https://github.com/tc39/proposal-relative-indexing-method

antris 5y ago

In addition to negative index support, a function is more easily composable e.g. converting a list of indices to a list of objects: `indices.map(myObjectArr.at)` I've lost count on how many times I've wrote this function manually.

bidirectional 5y ago
> `indices.map(myObjectArr.at)` That works in this case, but eta-reduction is not generally safe in Javascript due to the variadic nature of many functions, so I wouldn't recommend it in production code. For example `indices.forEach(console.log)` does not work as one would expect.
- antris 5y ago
  Better a function that works in some cases than not having a function at all. Also, by using TypeScript definitions you pretty much always know what's coming in and going out and VS Code will yell at you if you're trying to do something stupid.
  - e1g 5y ago
    A function that works in some cases will be a nightmare to debug. The pattern of `indices.map(myObjectArr.at)` is discouraged in JS because it often fails in unexpected ways. For example - ["1","2"].map(parseFloat) // works as expected ["1","2"].map(parseInt) // nope
    - antris 5y ago
      I've learned ages ago that parseInt cannot be used like this, so it's not a problem for me, but I thought linters already take care of this case? Also I wasn't talking about using parseInt, a broken function like this so I'm not sure what the quirks of old, widely known bad parts of Javascript have to do with using functions as arguments, which is one of the most powerful features of the language.
      - 5y ago