I have a function which takes four parameters, among which the 1st parameter is required, the 2nd & 3rd are optional, the 4th has a default value:
class MyClass {
static myFunc(param1: string, param2? : string, param3? : string, param4:boolean=true)
{
...
}
}
In my caller, I would like to provide the value of 1st parameter and override the 4th boolean. How to do that? I can't do MyClass.myFunc("foo", false). Should I re-design the function signature? What is the convention in TypeScript to have a function like that?
You should redefine the order and the usage of the parameters in your function.
Use param?:type
This way you can overload the function call without explicitly sending unnecessary undefined as arguments.
const func = (a:number, b:boolean = true, c?:string, d?:string) => {
console.log(a, b, c, d)
}
func(1)
func(1, false)
func(1, false, "Hello")
func(1, false, "Hello", "World")
In your case:
class MyClass {
static myFunc(param1:string, param2:boolean = true, param3?:string, param4?:string)
{
...
}
}
Here are a couple of ways to achieve the API you asked about:
class MyClass {
// the method in your question
static myFunc (
param1: string,
param2?: string,
param3?: string,
param4 = true,
): void {
console.log([param1, param2, param3, param4]);
}
// parameters reordered
static myRefactoredFunc (
param1: string,
param4 = true,
param2?: string,
param3?: string,
): void {
console.log([param1, param2, param3, param4]);
}
}
// if you can't modify the class, you can create a function with the
// parameters ordered by your preference, which calls the original method
// in the function body and returns its return value
const myFunc = (
param1: Parameters<typeof MyClass['myFunc']>[0],
param4?: Parameters<typeof MyClass['myFunc']>[3],
param2?: Parameters<typeof MyClass['myFunc']>[1],
param3?: Parameters<typeof MyClass['myFunc']>[2],
): ReturnType<typeof MyClass['myFunc']> => MyClass.myFunc(param1, param2, param3, param4);
// these are all equivalent
MyClass.myFunc('foo', undefined, undefined, false);
MyClass.myRefactoredFunc('foo', false);
myFunc('foo', false);