Implementing indexers in TypeScript to accommodate both string and numeric keys

Seeking to incorporate different types into existing code.

In the code, there exists a transitionData object in which objects can be added by index as shown below:

this.transitionData[id] = transition

where id is a number and transition is of type Transition.

Alternatively, it could be:

transitions[t].timer.stop()

Here, t is a string and timer is of type Timer.

The desired interface is as follows:

export interface TransitionData {
  [index: number]: Transition
  [key: string]: {timer: Timer}
}

However, TypeScript raises an issue with this setup:

Numeric index type 'Transition' cannot be assigned to string index type '{ timer: Timer; }

Answer №1

Combine two index signatures into a single entity.

interface TransitionMap {
    [index: number]: Transition
}

interface TimerMap {
    [index: string]: { timer: Timer }
}

declare const dataMerged: TransitionMap & TimerMap;

TypeScript will correctly interpret the data structure.

dataMerged["1"] // Timer
dataMerged[1]   // Transition

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