Creating a refined parameter type in Typescript using a discriminator

Question

Creating a refined parameter type in Typescript using a discriminator

Looking to work with a legacy API that has the following structure (playground link)...

type Command1 = {
    cmd: "my first command",
    arg1: string,
    arg2: boolean
}

type Command2 = {
    cmd: "my second command",
    foo: string,
    bar: number
}

type Command = Command1 | Command2

function execute(cmd: Command["cmd"], args:any /* would like to strongly type this */) {
    console.log(args)
}

execute("my first command", {/* oops missing props */})

Seeking a method to ensure type checking for the args parameter of the execute function without altering the function's parameter list. Any suggestions?

Appreciate any insights. Thank you.

typescript type-safety

Answer 1

Answer №1

Make sure to utilize the Extract<Type, Union> method by visiting this interactive playground:

function run<Task extends Job["task"]>(
  task: Task, 
  parameters: Omit<Extract<Job, { task: Task }>, "task">
) {
    console.log(task, parameters)
}

// run<"task A">(task: "task A",   parameters: Omit<Job1, "task">): void
run("task A", { param1: "value1", param2: true })

// run<"task B">(task: "task B", parameters: Omit<Job2, "task">): void
run("task B", { foo: "bar", baz: 123 })

Answer 2

Make sure to utilize the Extract<Type, Union> method by visiting this interactive playground:

function run<Task extends Job["task"]>(
  task: Task, 
  parameters: Omit<Extract<Job, { task: Task }>, "task">
) {
    console.log(task, parameters)
}

// run<"task A">(task: "task A",   parameters: Omit<Job1, "task">): void
run("task A", { param1: "value1", param2: true })

// run<"task B">(task: "task B", parameters: Omit<Job2, "task">): void
run("task B", { foo: "bar", baz: 123 })

Answer 3

Answer №2

Have you considered utilizing an intersection type with generics in this scenario? Assuming the remaining code aligns with your provided example:

function execute<T extends Command["cmd"]>(cmd: T, args: Command & { cmd: T }) {
    console.log(cmd, args)
}

It seems like a practical approach to effectively combine the discriminator and the appropriate type of Command.

Answer 4

Have you considered utilizing an intersection type with generics in this scenario? Assuming the remaining code aligns with your provided example:

function execute<T extends Command["cmd"]>(cmd: T, args: Command & { cmd: T }) {
    console.log(cmd, args)
}

It seems like a practical approach to effectively combine the discriminator and the appropriate type of Command.

Creating a refined parameter type in Typescript using a discriminator

Answer №1

Answer №2

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