Default parameters let callers omit values while still receiving sensible behavior. When you write width: number = 0, callers can pass just the string and the function will use 0.
You’ll implement left-padding: return the string with width spaces added on the left.
padLeft(s: string, width: number = 0): string.width is 0, return s unchanged.' '.repeat(width) + s.padLeft('x', 3) // ' x'
padLeft('x') // 'x'