Not sure if this is possible but I'd like to write a function where I take in a string and an object.
The type of the second object should contain a property with a name that is the same as the before mentioned string and have a certain type.
E.g.
// No error
someFuncion("foo", {foo: 42})
// Error
someFuncion("foo", {foo: "a string instead of a number"})
someFuncion("foo", {bar: 42})
Can anyone show me what the type signature for this function would be please?
Thanks
I think what you are looking for is a generic function with a default generic type.
function someFunction<T extends string>(param1: T, param2: Record<T, number>) {}
string = string bit? I come from a C# background so restricting a generic param to a certain type makes sense so I understand T extends string but it's the following equals that throws me a bit.
You can achieve that very easily using interfaces.
The function must accept a string and an object.
Using Typescript interfaces (suggested):
The parameters of obj must follow the interface IObject.
interface IObject {
foo: number;
};
function someFunction(str: string, obj: IObject): void {
// ...
}
Without interface declaration "inline":
function someFunction(str: string, obj: { foo: number }): void {
// ...
}
Now if you try to run the examples you will get:
someFuncion("foo", {foo: 42}) -> NO ERRORsomeFuncion("foo", {foo: "a string instead of a number"}) -> Type 'string' is not assignable to type 'number'.someFuncion("foo", {bar: 42}) -> Argument of type '{ bar: number; }' is not assignable to parameter of type '{ foo: number; }'. Object literal may only specify known properties, and 'bar' does not exist in type '{ foo: number; }.