Description
Search Terms:
confusing, pick, description
Problem:
Typescript has so much great functionality, but it gets hard to comprehend them for a not very experienced developer if the descriptions are confusing. Example is the description of Pick mapped property.
Actual behavior:
The description of type Pick<T, K extends keyof T> = { [P in K]: T[P]; }says:
From T pick a set of properties K.
However, the way I have been assuming the description at first, before I discovered the truth, was: we need to supply a defined type / interface as a first parameter and another defined type / interface as a second parameter, i.e.:
type ParamOne = {
one: string;
two: string;
three: number;
}
type ParamTwo = {
two: string;
three: number;
}
type Picked = Pick<ParamOne, ParamTwo> // error
This does not work and would lead to the error, because the second parameter should contain the keys of ParamOne delineated with |, even though the description says a set of !properties K, not a set of !keys K. I understand that the word propertiesprobably refers to T, but hear me out.
So, the correct way to get type { two: string, three: number }would be this way:
type Picked = Pick<ParamOne, 'two' | 'three'>
Expected behavior:
Therefore, instead of having:
From T pick a set of properties K.
as a description, would not it be more clearer, especially for the not very experienced developers, if the description would change to:
From T pick a set of properties whose keys are K.
?
I understand that there is also the definition of the type available for us which looks this way:
type Pick<T, K extends keyof T> = { [P in K]: T[P]; }
But for me as a person who has not been working with typescript for a lot of time, this looked like very complicated and unfamiliar syntax when perceived altogether in a single line, even though some parts, like the one to the right, where the object property is being assigned, were more or less readable.
I hope that future generations of typescript users won't be struggling with mapped types the way I have been and this correction might improve the situation. Thank you!