Svelte 5: Monkeypatching introduced in #11610 has broken array_prototype.lastIndexOf()

[marklbarlow]

Describe the bug

The introduction of equality.js in #11610 seems to have broken the behaviour of lastIndexOf() from 5.0.0-next.134 onwards.

Specifically, from v134 omitting the second argument (fromIndex) seems to default as 0 / falsy rather than the last index of the array.

const arr = [0, 1, 2];
console.log('Without fromIndex:', arr.lastIndexOf(2));
console.log('With fromIndex:', arr.lastIndexOf(2, arr.length - 1));

Before:

Without fromIndex: 2
With fromIndex: 2

After:

Without fromIndex: -1
With fromIndex: 2

Thanks for all the hard work on this. Looking forward to the final release.

Reproduction

As above.

Logs

No response

System Info

System:
    OS: macOS 11.7.10
    CPU: (4) x64 Intel(R) Core(TM) M-5Y71 CPU @ 1.20GHz
    Memory: 49.04 MB / 8.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 20.3.0 - /usr/local/bin/node
    npm: 9.6.7 - /usr/local/bin/npm
  Browsers:
    Chrome: 124.0.6367.210
    Safari: 16.6.1
  npmPackages:
    svelte: ^5.0.0-next.134 => 5.0.0-next.134

Severity

blocking all usage of svelte