Implement Array.prototype.filter and Array.prototype.find

[robertDurst]

For both of these, I use JsValue to capture a function as input -- which is possible since functions are values in JS. However, these fail if the user does not input a function. What is the recommended way to safe guard against this? Should I use the #[wasm_bindgen(catch)] with -> Result<JsValue, JsValue>?

[jonathan-s]

Yeah, I would say that is a good idea, since filter will throw an error if it is not a function in normal javascript. You can have a look at #299 for how I handled the case of Result in the tests as an example perhaps.

[robertDurst]

@jonathan-s ah I see. Will implement something similar. Thanks!

[robertDurst]

Hmm looks like I will need to return Result<Array, JsValue> for Array.prototype.filter which is not yet implemented.

[fitzgen]

For both of these, I use JsValue to capture a function as input -- which is possible since functions are values in JS. However, these fail if the user does not input a function. What is the recommended way to safe guard against this? Should I use the #[wasm_bindgen(catch)] with -> Result<JsValue, JsValue>?

For type mismatch errors that we can statically ensure we won't ever trigger via Rust's type system, there is no need to catch. For example, if we make Array.prototype.filter take a function argument instead of a JsValue argument at the type level, we know that Rust code can never pass a Number to filter and that the type error will never be thrown.

If we are going the other way -- exporting a Rust function that takes a JS function as input (which is also not even implemented yet) -- then we do have to do the dynamic type checks because there is no statically typed compiler checking the JS side of things, like there is on the Rust side in the previous example.

[fitzgen]

I think we should make these take functions as input rather than JsValue, see https://rustwasm.github.io/wasm-bindgen/closures.html for details.

[robertDurst]

Ah yes @fitzgen thanks that makes a lot more sense.

This makes more sense logically:

pub fn find(this: &Array, function: &Fn(JsValue) -> bool) -> JsValue;

However, I end up getting this error:

the trait `wasm_bindgen::convert::RefFromWasmAbi` is not implemented for `std::ops::Fn(wasm_bindgen::JsValue) -> bool + 'static`

which, if I remember correctly @jonathan-s also received.

[jonathan-s]

Yeah, got that too

On Sun 24. Jun 2018 at 01:41, Robert Durst ***@***.***> wrote: Ah yes @fitzgen <https://github.com/fitzgen> thanks that makes a lot more sense. This makes more sense logically: pub fn find(this: &Array, function: &Fn(JsValue) -> bool) -> JsValue; However, I end up getting this error: the trait `wasm_bindgen::convert::RefFromWasmAbi` is not implemented for `std::ops::Fn(wasm_bindgen::JsValue) -> bool + 'static` which, if I remember correctly @jonathan-s <https://github.com/jonathan-s> also received. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#300 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ACBsEjUSSZm83qUIgtA8N5XuvMaCOohIks5t_tI6gaJpZM4U03uC> .

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[akryvomaz]

I can confirm this error. Also tried with Closure<Fn()>, &Closure<FnMut()> etc.

[robertDurst]

What is the solution here? Should we implement
wasm_bindgen::convert::RefFromWasmAbi` for `std::ops::Fn(wasm_bindgen::JsValue) -> bool + 'static?

[fitzgen]

I'm not 100% sure -- I need to dig in a little more to figure out why the existing function support isn't working here.

[robertDurst]

Closing for now since Array.prototype.filter was implemented in #314