const obj = { wheels: 4, lights: 2, doors: 4 }
customMapFunction(obj, {
properties: ["wheels", "lights"],
formatter: (wheels, lights) => `${wheels}-${lights}` // "4-2"
})
How do I define the types for customMapFunction in TypeScript to ensure that properties are keys of obj and that the formatter function will accept all the values referenced by the elements in the properties array within obj?
To create a function with specific parameters, you can use the following syntax:
function someCustomFunction<
T,
K extends (keyof T)[]
>(object: T, propertiesAndFormat: {
properties: [...K],
format: (...arguments: {
[index in keyof K]: T[K[index]]
}) => string
}) {
return null!
}
The function has two generic parameters referred to as T and K. The T parameter indicates the type of the object passed as object, while K represents a tuple of keys from T. When specifying the type for the properties parameter, the variadic tuple notation [...K] is used to recognize K as a tuple rather than an array due to the significance of order.
Regarding the format parameter, it is defined as a rest parameter where the order and type of elements are determined by a tuple. This tuple is created by iterating over the elements denoted by I in the tuple
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