> Before JavaScript it was impossible to make this mistake Before JavaScript it was impossible to even implement such functionality on the client side... Ther

> Before JavaScript it was impossible to make this mistake Before JavaScript it was impossible to even implement such functionality on the client side... There was no "number" input before HTML5 spec which came out in 2008, and was adopting for 6 years before finally becoming a recommendation in 2014. You had to let user put any text in the input and do the validation on the backend, which had the same Turing complete language running letting you make any mistakes you want. Rule of least power is just a design principle, and it could not hold as an axiom of good design for the web, because when the least power becomes not enough power, it takes years for the adoption of new powers needed – that's why JavaScript exists in the first place.