0
232
ViewsTypescript function param with interface object array & string array
I am trying to create a Typescript function that have a parameter with an interface of Object[] or string[].
interface NameObj {
val: string
}
const myFunc = function(names : NameObj[] | string[], toFind: string) {
return names.find(name => name.val === toFind || name === toFind );
}
const list = ['app', 'test', 'ben']
console.log(myFunc(list, 'ben'))
Lint Error 
but I am getting an Lint error in find(name => ...) of
Parameter 'name' implicitly has an 'any' type.'
Typescript playground Link Sample Code
1 answers
Answer question0
The reason for this error is that names might be either an array of NameObj (NameObj[]) or an array of strings (string[]), and while both provide a function find, NameObj[].find returns NameObj | undefined and string[].find returns string | undefined, so the compiler don't now which type to use.
The are different ways to handle this. I would prefer the use of generics. This way you tell the compiler that we can input either NameObj[] or string, and whichever it is, that's also the type returned.
const myFunc = function<T extends NameObj | string>(names : T[], toFind: string) {
return names.find(name => typeof name === "object" ? name.val === toFind : name === toFind);
}
In the above code I also changed the function to name => typeof name === "object" ? name.val === toFind : name === toFind . With your previous implementation, you get an error since name might be a string and thus name.val is invalid. This checks the type first.