What is the process for invoking instance methods dynamically in TypeScript?

Question

What is the process for invoking instance methods dynamically in TypeScript?

There is an object in my possession and the goal is to dynamically invoke a method on it.

It would be ideal to have typechecking, although that may prove to be unattainable. Unfortunately, the current situation is that I cannot even get it to compile:

  const key: string = 'someMethod'
  const func = this[key]
  func(msgIn)

leads to the following error message...

Element implicitly has an 'any' type 
because expression of type 'any' can't be used 
to index type 'TixBot'.

I experimented with other type options but none were successful.

  const key: any = cmd.func
  const func: any = this[key]

Aside from @ts-ignore, are there alternative solutions? I am considering utilizing .call() or bind as potential workarounds?

typescript methods dynamic-programming dispatch

Answer 1

Answer №1

When using Typescript, it will throw an error if it cannot verify that the string being used is a valid member of the class. An example of this working correctly would be:

class MyClass {
    methodA() {
        console.log("A")
    }
    methodB() {
        console.log("B")
    }

    runOne() {
        const random = Math.random() > 0.5 ? "methodA" : "methodB" // random is typed as "methodA" | "methodB"
        this[random](); //ok, since random is always a key of this
    }
}

In the above examples, omitting the explicit type annotation from a constant will give you the literal type and enable you to use the const as an index into this.

You can also specify the string as keyof Class:

class MyClass {
    methodA() {
        console.log("A")
    }
    methodB() {
        console.log("B")
    }

    runOne(member: Exclude<keyof MyClass, "runOne">) { // exclude this method
        this[member](); //ok
    }
}

If you already have a string, you can use an assertion to keyof MyClass, although this may not be as type safe (this[member as keyof MyClass] where let member: string)

Answer 2

When using Typescript, it will throw an error if it cannot verify that the string being used is a valid member of the class. An example of this working correctly would be:

class MyClass {
    methodA() {
        console.log("A")
    }
    methodB() {
        console.log("B")
    }

    runOne() {
        const random = Math.random() > 0.5 ? "methodA" : "methodB" // random is typed as "methodA" | "methodB"
        this[random](); //ok, since random is always a key of this
    }
}

In the above examples, omitting the explicit type annotation from a constant will give you the literal type and enable you to use the const as an index into this.

You can also specify the string as keyof Class:

class MyClass {
    methodA() {
        console.log("A")
    }
    methodB() {
        console.log("B")
    }

    runOne(member: Exclude<keyof MyClass, "runOne">) { // exclude this method
        this[member](); //ok
    }
}

If you already have a string, you can use an assertion to keyof MyClass, although this may not be as type safe (this[member as keyof MyClass] where let member: string)

What is the process for invoking instance methods dynamically in TypeScript?

Answer №1

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