string.js

function sample(x) {
    if (typeof x !== "number") {
        console.log("die");
        return;
    }
    console.log(x);
}
console.log(typeof "123");
console.log(typeof "123.0");
console.log(typeof 123.0);
console.log(typeof 123);
sample(123);
sample("123");

string.ts

function sample(x: Number) {
    if(typeof x !== "number") {
        console.log("die");
        return;
    }
    console.log(x);
}
console.log(typeof "123");
console.log(typeof "123.0");
console.log(typeof 123.0);
console.log(typeof 123);
sample(123);
sample("123");