JavaScript determines whether a number is prime

Determine if the user is entering a prime number

Const ReadLine = require ("Readline-sync"); Console.log ("Please enter a number:"= readline.question ()-0;  while (IsNaN (num) | | num <= 0) {    console.log ("input error, please re-enter")    ; = Readline.question ()-0;}  while (num = = 1) {    console.log ("1 is neither prime nor composite");     = Readline.question ()-0;    }

Method one: from 2 to num-1 number, find can be divisible by num number, find that num is not prime, otherwise it is prime

Let a = 0; // for temporary counting  for (Let i = 2; i < num; i++) {   if (num% i = = 0) {       console.log (num+ "not Prime");       A++       ;  Break ;   }} if (A = = 0)    {+ "is prime");}

Method Two: The number from 2 to NUM, the number that can be divisible by num, if this number equals num,num is prime, otherwise it is not prime

 for (Let i = 2; I <= num; i++) {    if(num% i = = 0)       {if (num = = i) {           + "is prime");       } Else {           + "not prime number")           ;  Break ;       }    }}

Method Three: from 1 to num, look for numbers divisible by num, find the Count 1 times, the final number if 2,num is prime, otherwise it is not prime

Let B = 0;  for (Let i = 1; I <= num; i++) {    if (num% i = = 0) {        b+ +;    }} if (b = = 2)    {+ "is prime");} Else {    + "not prime number");}

JavaScript determines whether a number is prime