如何使用typescript未知的运行时变量？

let unknownVariable: any;

unknownVariable = "Hello, World!";
unknownVariable = 42;

let unknownVariable: unknown;

unknownVariable = "Hello, World!";
unknownVariable = 42;

// 使用前必须进行类型检查
if (typeof unknownVariable === "string") {
    console.log(unknownVariable.toUpperCase());
} else if (typeof unknownVariable === "number") {
    console.log(unknownVariable.toFixed(2));
}

let unknownVariable: unknown;

unknownVariable = "Hello, World!";

// 类型断言
const str = unknownVariable as string;
console.log(str.toUpperCase());

function processValue<T>(value: T): void {
    if (typeof value === "string") {
        console.log(value.toUpperCase());
    } else if (typeof value === "number") {
        console.log(value.toFixed(2));
    } else {
        console.log("Unknown type");
    }
}

processValue("Hello, World!");
processValue(42);

function assertNever(x: never): never {
    throw new Error("Unexpected object: " + x);
}

function processValue(value: string | number): void {
    if (typeof value === "string") {
        console.log(value.toUpperCase());
    } else if (typeof value === "number") {
        console.log(value.toFixed(2));
    } else {
        assertNever(value);
    }
}