TypeScript or JavaScript?

test.ts

// If this code is transpiled by the TypeScript compiler, it will echo "You are using TypeScript"
// If this code is ran as-is, it will echo "You are using JavaScript"

console.log(new Set<String>('1') ? 'You are using TypeScript' : 'You are using JavaScript')

// This is actually valid JavaScript code: properly formatted, it looks like that:
// (new Set) < (String) > ('1')

// In TypeScript, the angle brackets after Set are interpreted as generic types, which is why the result is different.