substr () method can extract in the string specified number of characters from the start subscript,

StringObject. Substr (start, length)
1 kind of use the substr () directly extract

<script>

Var card=(prompt (" please enter the id number));

YearB=card. Substr (6, 4);

The console. The log (yearB);

YearB=2021 - yearB;



The switch (yearB> 18)={
Case true:

Alert (' your id number is: + card + '\ n' + "this year you + yearB + years old, adult, boot success!!!!! ");

break;

Case false:

Alert (' your id number is: + card + '\ n' + "this year you + yearB + years old, is a minor, suggest to find id card!!!!! ");

break;

}

</script>

The second use division



<meta charset="utf-8" & gt;

<meta HTTP - equiv="X - UA - Compatible" content="IE=edge" & gt;

<meta name="viewport" content="width=device - width, initial - scale=1.0" & gt;