TypeScript Type for function arguments not erroring?

I'm attempting to define what arguments must be passed to a function in React with Typescript:

type IncrementDecrementFunctionArgs = {
  id: number;
  amount: string;
  foo: string;
};

export const dummyProps = {
  increment: function({ id, amount }: IncrementDecrementFunctionArgs) {
    console.log("increment ", id, " by amount: ", amount);
  }
}

Props are spread into component:

<Component {...dummyProps} />  

Component calls function:

  const handleClick = (val: incrementDecrement) => {
    if (val === incrementDecrement.increment) {
      increment({ id, amount });
    } else {
      decrement({ id, amount });
    }
  };

I can't work out why this isn't erroring. foo does not exist. id is a string and amount is a number.