how to dynamically call instance methods in typescript?

Typescript will error if it can't check that the string used is a valid member of the class. This for example will work:

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 samples above removing the explicit type annotation from a constant should give you the literal type and allow you to use the const to index into this.

You could also type 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 using an assertion to keyof MyClass is also an option although this is not as type safe (this[member as keyof MyClass] where let member: string)