Command Dispatch Case

A discriminated command type keeps each action branch visible.

commands.ts

type Command =
    | { kind: "add"; amount: number }
    | { kind: "subtract"; amount: number }
    | { kind: "reset" };

function applyCommand(total: number, command: Command): number {
    if (command.kind === "add") {
        return total + command.amount;
    }

    if (command.kind === "subtract") {
        return total - command.amount;
    }

    return 0;
}

const useReset: boolean = ;
const commands: Command[] = [
    { kind: "add", amount: 5 },
    useReset ? { kind: "reset" } : { kind: "subtract", amount: 2 },
    { kind: "add", amount: 3 }
];

let total: number = 0;
for (const command of commands) {
    total = applyCommand(total, command);
}

console.log(`total=${total}`);

type Command =
    | { kind: "add"; amount: number }
    | { kind: "subtract"; amount: number }
    | { kind: "reset" };

function applyCommand(total: number, command: Command): number {
    if (command.kind === "add") {
        return total + command.amount;
    }

    if (command.kind === "subtract") {
        return total - command.amount;
    }

    return 0;
}

const useReset: boolean = ;
const commands: Command[] = [
    { kind: "add", amount: 5 },
    useReset ? { kind: "reset" } : { kind: "subtract", amount: 2 },
    { kind: "add", amount: 3 }
];

let total: number = 0;
for (const command of commands) {
    total = applyCommand(total, command);
}

console.log(`total=${total}`);

command dispatch Dispatching by command kind is a traceable way to apply several updates in order.