Add Array.prototype.findLast and Array.prototype.findLastIndex

lib Update Request

Configuration Check

My compilation target is ES5 and my lib is ESNext.

Missing / Incorrect Definition

Missing Array.prototype.findLast and Array.prototype.findLastIndex

Sample Code

[3, 2, 1].findLast(x => x > 2);

Documentation Link

Proposal: https://tc39.es/proposal-array-find-from-last/ (currently stage 3 4)
Can I Use: https://caniuse.com/mdn-javascript_builtins_array_findlast (Chrome and Safari already shipped it without flags)

Daniel Rosenwasser (@DanielRosenwasser)

[Double checking with Daniel Rosenwasser (@DanielRosenwasser) that stage 3 is the only criteria for adding to lib.esnext]

It is, but if I ask for stage 4 at an upcoming meeting we might as well add it to a stable version.

Seems weird that Firefox hasn’t implemented it yet, that’s a bit unfortunate.

Seems weird that Firefox hasn’t implemented it yet, that’s a bit unfortunate.

Sorry....My fault.

Wenlu Wang (@Kingwl)

Wenlu Wang (@Kingwl) It’s your fault that Firefox doesn’t support this API? What?

Bruce Pascoe (@fatcerberus)

Bruce Pascoe (@fatcerberus), the context is that Wenlu Wang (@Kingwl) is contributing the changeset to Firefox.

By the way, we reached Stage 4 today! 🎉🎉🎉

I believe that means we should add this to lib.es2023.array.d.ts.

With which version of typescript I could use the method findLast?

Upgrade typescript to 5.0.x to use Array.findLast()

It works on TypeScript 5 at least at the playground typescriptlang.org: example. It doesn't say much though: it also works just fine if you select Typescript 4.

Also note that you'll need at least Node.JS 18, as that's the lowest version that supports findLast (source).

It works only in TS 5 and only when the target is ESNext.

Cristan Meijer (@cristan)

Cristan Meijer (@cristan) It works on TypeScript 5 at least at the playground typescriptlang.org

Incorrect, as you can see here:

As Sergii Bondarenko (@BR0kEN-) said, if you change the target in that environment, the issue disappears. But if you try to "Export" the example to CodeSandbox with the same settings, it triggers the issue again.

Tried also updating to the latest Typyscript 5.1 build, no change.

Remove custom type annotation for `Array.prototype.findLast`

(focus-trap/src/global.d.ts) Remove custom type annotation for `Array…

findLast was introduced in EcmaScript 2023. However, es2023 isn't supported in Typescript 5. Maybe that's it?

Is there any progress with this issue?

Is there any progress on this issue?

There's not progress because it was fixed in 2022. If you're not seeing findLast / etc, you have a configuration issue. Seek support at StackOverflow, Discord, etc.

Ah, it indeed does work, but the problem is indeed that findLast was introduced in EcmaScript 2023. You'll need Node.JS 18 or higher for that, but that that isn't much of a problem. TypeScript is slightly more problematic:

Setting the target to es2023 even in TypeScript 5.3.3 yields the same error I had before. However, findLast does work when setting the target to esnext ^_^

In the handbook, you'll see that es2023 is indeed not an option. It also states: "esnext is a moving target that may include support for Stage 3 proposals to ECMAScript modules". So I would much rather set the target explicitly to es2023 instead to this vague concept, but hey, it works.

here is the solution

make the declaration under your code with findLastIndex

Array.prototype.findLastIndex = function(predicate) { for (let i = this.length - 1; i >= 0; i--) { if (predicate(this[i], i, this)) { return i; } } return -1; };

and it will fix your issue

Compile Error Line 31: Char 32: error TS2550: Property 'findLastIndex' does not exist on type 'string[]'. Do you need to change your target library? Try changing the 'lib' compiler option to 'es2023' or later.

Got above on my LeetCode solution https://leetcode.com/problems/increasing-decreasing-string

MDN says

"Baseline 2022 Newly available Since August 2022, this feature works across the latest devices and browser versions. This feature might not work in older devices or browsers."

So I guess that's why. Leetcode yet to update their transpiler/compiler

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Add `Array.prototype.findLast` and `Array.prototype.findLastIndex` #48829

lib Update Request

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Add Array.prototype.findLast and Array.prototype.findLastIndex #48829

Description

lib Update Request

Configuration Check

Missing / Incorrect Definition

Sample Code

Documentation Link

Activity

andrewbranch commented on Apr 25, 2022

DanielRosenwasser commented on Apr 26, 2022

fatcerberus commented on Apr 27, 2022

Kingwl commented on Apr 28, 2022

fatcerberus commented on Apr 28, 2022

DanielRosenwasser commented on Jun 6, 2022

monikams commented on Oct 12, 2022

16 remaining items

cristan commented on Apr 13, 2023

BR0kEN- commented on Apr 18, 2023

juneate commented on Apr 25, 2023

cristan commented on Jun 26, 2023

shakedhagag commented on Sep 13, 2023

jacobbogers commented on Oct 26, 2023

RyanCavanaugh commented on Oct 26, 2023

cristan commented on Dec 19, 2023

GoRRRRchik commented on Feb 20, 2024

traez commented on Sep 18, 2024

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Add `Array.prototype.findLast` and `Array.prototype.findLastIndex` #48829