How to keep value as number in JSON.stringify()

toFixed returns a string. If you want to output a number, just use parseFloat:

JSON.stringify({
  "payer": "a cat",
  "price": parseFloat(amount)
});

I don't think there's a way to output a number to any precision after the decimal without converting it to a string.

I think Number() will work too

The differences are here. I have worked with both in JSON.stringify

var data = JSON.stringify({
  "payer": "a cat",
  "price": Number(amount)
});