undefined | Better HN

0 pointsdevit5y ago0 comments

A function like this should not be something that anyone even thinks of writing or using.

In properly designed languages, values have either a known concrete type, or the interfaces that they have to support are listed, and the compiler checks them.

Even in JavaScript/TypeScript, if you are using this, you or a library you are using are doing it wrong, since you should know whether a value is a promise or not when writing code.

0 comments

city415y ago

This function is most likely an artifact of before promises got standardized. One way promises took off and became so ubiquitous is different implementations could interop seamlessly. And the reason for that is a promise was defined as 'an object or function having a then method which returns a promise when called'.

Doesn't excuse the JS ecosystem and JS as a whole, which truly is a mess. But there's a history behind these things.

stefan_5y ago

I think the point of the comment is: you should not be testing for this at all.

If your API works with promises, call .then() on what is handed to you. That's it. Don't make up emergent, untestable behavior on the spot.

city415y ago

You need to do this test if you are creating a promise implementation. That was my point, there is a reason code like this exists.

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0 pointsdevit5y ago0 comments

A function like this should not be something that anyone even thinks of writing or using.

In properly designed languages, values have either a known concrete type, or the interfaces that they have to support are listed, and the compiler checks them.

Even in JavaScript/TypeScript, if you are using this, you or a library you are using are doing it wrong, since you should know whether a value is a promise or not when writing code.

0 comments

city415y ago

Doesn't excuse the JS ecosystem and JS as a whole, which truly is a mess. But there's a history behind these things.

stefan_5y ago

I think the point of the comment is: you should not be testing for this at all.

If your API works with promises, call .then() on what is handed to you. That's it. Don't make up emergent, untestable behavior on the spot.

city415y ago

You need to do this test if you are creating a promise implementation. That was my point, there is a reason code like this exists.

1 more reply

j / k navigate · click thread line to collapse