Erased Syntax

// --- debugger: a no-op (no attached inspector), matching plain JS ---
const start = 1
debugger
console.log(start)            // 1

// --- readonly array / tuple types: modifier erased, immutability not enforced ---
const nums: readonly number[] = [10, 20, 30]
console.log(nums[0] + nums[2])   // 40

function total(xs: readonly number[]): number {
  let s = 0
  for (const x of xs) s += x
  return s
}
console.log(total(nums))         // 60

const pair: readonly [number, string] = [7, "seven"]
console.log(`${pair[0]}=${pair[1]}`)   // 7=seven

// --- explicit `this` parameter: erased; real args bind by their own positions ---
function label(this: void, name: string, n: number): string {
  return `${name}:${n}`
}
console.log(label("edges", 12))  // edges:12

// --- old-style angle-bracket type assertion: erased like `as T` ---
const casted = <number>21
console.log(<number>casted * 2)  // 42

// --- numeric-literal types: resolve to number, value not narrowed ---
type Direction = -1 | 0 | 1
const dir: Direction = 1
console.log(dir * 10)            // 10

// --- generic function types: <T>(x: T) => T erases T to any ---
var idf: <T>(x: T) => T
idf = (x: any): any => x
console.log(idf("erased"))       // erased

// --- type predicates: `x is T` returns are booleans; narrowing not modeled ---
function isShort(s: string): s is string {
  return s.length < 4
}
console.log(isShort("hey"))      // true