Validate date of birth, so you can not register under 18 years (Javascript)

Question

I have a field called txtdata_nasc of the date type. I need the user not to be able to type a date that makes him less than 18 years old, but also that he cannot be of an absurd age, such as 100 years old, I need him to be able to type at most a date of birth that makes him 60 years old. For example, it cannot type (using today’s example, 05/05/2018) a date greater than '05/05/2000' and a date shorter than 05/05/1958.

Answer 1

A simple solution to validate if the person is more or less 18 years old is to create a date with the same month and day, and with the year added up to 18. Then you just need to compare whether that date is shorter or longer than the current date.

Example:

const inputNasc = document.getElementById("txtdata_nasc");

document.querySelector("form").addEventListener("submit", function(){
  //obter array com [ano,mes,dia] através de split("-") e convertendo em numero com Map
  let nasc = inputNasc.value.split("-").map(Number);
  //construir data 18 anos a seguir a data dada pelo usuario
  let depois18Anos = new Date(nasc[0] + 18, nasc[1] - 1, nasc[2]);
  let agora = new Date();
  
  if (depois18Anos <= agora){
    console.log("Maior de 18");
  }
  else {
    console.log("Menor de 18");
  }
  event.preventDefault(); //só para não mudar de pagina na submissão do formulario
});

<form>
  <input type="date" id="txtdata_nasc">
  <input type="submit" value="Validar">
</form>

It is important to note that as Javascript months start at zero, the part of the month has to be subtracted from 1 with nasc[1] - 1.

To validate for less than 100 years can use exactly the same principle, changing only in comparison:

let nasc = inputNasc.value.split("-").map(Number);
let depois18Anos = new Date(nasc[0] + 18, nasc[1] - 1, nasc[2]);
let depois100Anos = new Date(nasc[0] + 100, nasc[1] - 1, nasc[2]);
let agora = new Date();

if (depois18Anos > agora){
  console.log("Menor de 18");
}
else if(depois100Anos < agora){
  console.log("Maior de 100");
}
else {
  console.log("valido");
}

With destructuring assignment can make the construction of dates X years ahead simpler and clearer:

let [ano, mes, dia] = inputNasc.value.split("-").map(Number);
//    ^----^----^--- Destructuring assignment
let depois18Anos = new Date(ano + 18, mes - 1, dia);
let depois100Anos = new Date(ano + 100, mes - 1, dia);