Fix Array.prototype.copyWithin polyfill

[teppeis]

Improvement:

• should handle negative params
• should coerce params to integer
• fix bug in deleting props of ArrayLike
• should throw if this is null or undefined
• should throw if impossible to delete props

Also this fixes .name and .length with defineProperty.
But if the policy of Closure Compiler for them is "won't fix", I will revert them.

I don't know how to run polyfill tests (#1504), but I confirmed this passed all Test262 tests for copyWithin. (https://gist.github.com/teppeis/c8a88f653cdd70ed3e3d6597ec1ee30c)

Ref:

• https://www.ecma-international.org/ecma-262/8.0/#sec-array.prototype.copywithin
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/copyWithin

[brad4d]

@shicks could you review this one, since polyfills are really your thing?

[brad4d]

Created internal issue b/122075328

[shicks]

Sorry for the long delay - I didn't see this until Bradford pinged me on the internal bug.

[teppeis]

@shicks Thanks! I've fixed and commented, please review them.
I'll rebase on latest master if you want.

[shicks]

I'm not super familiar with the github code review tools - I marked two conversations as unresolved, so hopefully you'll see my responses now.

[tjgq]

This test no longer passes. Please remove it.

[teppeis]

Really? It should be pass and I believe it passes.

this is null and this.length is referred on the top of the polyfill function, so it should throw an error.
https://github.com/google/closure-compiler/pull/2902/files#diff-a5e0f0788d56ad46f3db1223fd3c8b5cR36

[tjgq]

I didn't look close enough: it fails because the start and target arguments are not optional (unfortunately, I don't think there's a way to run the polyfill tests externally, so there's no way for you to reproduce it). The best you can do is something like this:

Array.prototype.copyWithin.call(null, some_other_array, 0);

[teppeis]

@tjgq understood. It is not a runtime test, but a type check failed. I added the second and the third argument.

[tjgq]

Same as above.

[teppeis]

@tjgq Probably type check in 2nd arg of Object.defineProperty() failed, so I fixed it.

[teppeis]

@tjgq Thanks! 😸