interface SquareConfig { color?: string; width?: number; } function createSquare(config: SquareConfig): { color: string; area: number } { let newSquare = {color: "white", area: 100}; if (config.clor) { // Error: Property 'clor' does not exist on type 'SquareConfig' newSquare.color = config.clor; } if (config.width) { newSquare.area = config.width * config.width; } return newSquare; } let mySquare = createSquare({color: "black"});