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How to determine if a number is odd in JavaScript

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一向 2020-11-27 10:05

Can anyone point me to some code to determine if a number in JavaScript is even or odd?

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27条回答
  • 失恋的感觉
    2020-11-27 10:37

    Use the below code:

    function isOdd(num) { return num % 2;}
console.log("1 is " + isOdd(1));
console.log("2 is " + isOdd(2));
console.log("3 is " + isOdd(3));
console.log("4 is " + isOdd(4));

    1 represents an odd number, while 0 represents an even number.

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  • 时光取名叫无心
    2020-11-27 10:39

    Like many languages, Javascript has a modulus operator %, that finds the remainder of division. If there is no remainder after division by 2, a number is even:

    // this expression is true if "number" is even, false otherwise
(number % 2 == 0)

    This is a very common idiom for testing for even integers.

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  • 轮回少年
    2020-11-27 10:39

    Just executed this one in Adobe Dreamweaver..it works perfectly. i used if (isNaN(mynmb))

    to check if the given Value is a number or not, and i also used Math.abs(mynmb%2) to convert negative number to positive and calculate

        <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>

</head>
<body bgcolor = "#FFFFCC">
    <h3 align ="center"> ODD OR EVEN </h3><table cellspacing = "2" cellpadding = "5" bgcolor="palegreen">
        <form name = formtwo>
            <td align = "center">
                <center><BR />Enter a number: 
                    <input type=text id="enter" name=enter maxlength="10" />
                    <input type=button name = b3 value = "Click Here" onClick = compute() />
                      <b>is<b> 
                <input type=text id="outtxt" name=output size="5" value="" disabled /> </b></b></center><b><b>
                <BR /><BR />
            </b></b></td></form>
        </table>

    <script type='text/javascript'>

        function compute()
        {
          var enter = document.getElementById("enter");
          var outtxt = document.getElementById("outtxt");

          var mynmb = enter.value;
          if (isNaN(mynmb)) 
          { 
            outtxt.value = "error !!!"; 
            alert( 'please enter a valid number');
            enter.focus();
            return;
          }
          else 
          { 
             if ( mynmb%2 == 0 ) { outtxt.value = "Even"; }  
             if ( Math.abs(mynmb%2) == 1 ) { outtxt.value = "Odd"; }
          }
        }

    </script>
</body>
</html>
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  • Happy的楠姐
    2020-11-27 10:42

    Many people misunderstand the meaning of odd

    • isOdd("str") should be false.
      Only an integer can be odd.
    • isOdd(1.223) and isOdd(-1.223) should be false.
      A float is not an integer.
    • isOdd(0) should be false.
      Zero is an even integer (https://en.wikipedia.org/wiki/Parity_of_zero).
    • isOdd(-1) should be true.
      It's an odd integer.

    Solution

    function isOdd(n) {

  // Must be a number
  if (isNaN(n)) {
    return false;
  }

  // Number must not be a float
  if ((n % 1) !== 0) {
    return false;
  }

  // Integer must not be equal to zero
  if (n === 0) {
    return false;
  }

  // Integer must be odd
  if ((n % 2) !== 0) {
    return true;
  }

  return false;
}

    JS Fiddle (if needed): https://jsfiddle.net/9dzdv593/8/

    1-liner

    Javascript 1-liner solution. For those who don't care about readability.

    const isOdd = n => !(isNaN(n) && ((n % 1) !== 0) && (n === 0)) && ((n % 2) !== 0) ? true : false;
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  • 旧巷少年郎
    2020-11-27 10:43

    Do I have to make an array really large that has a lot of even numbers

    No. Use modulus (%). It gives you the remainder of the two numbers you are dividing.

    Ex. 2 % 2 = 0 because 2/2 = 1 with 0 remainder.

Ex2. 3 % 2 = 1 because 3/2 = 1 with 1 remainder.

Ex3. -7 % 2 = -1 because -7/2 = -3 with -1 remainder.

    This means if you mod any number x by 2, you get either 0 or 1 or -1. 0 would mean it's even. Anything else would mean it's odd.

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  • Happy的楠姐
    2020-11-27 10:43 
       <script>
        function even_odd(){
            var num =   document.getElementById('number').value;

            if ( num % 2){
                document.getElementById('result').innerHTML = "Entered Number is Odd";
            }
            else{
                document.getElementById('result').innerHTML = "Entered Number is Even";
            }
        }
    </script>
</head>
<body>
    <center>
        <div id="error"></div>
        <center>
            <h2> Find Given Number is Even or Odd </h2>
            <p>Enter a value</p>
            <input type="text" id="number" />
            <button onclick="even_odd();">Check</button><br />
            <div id="result"><b></b></div>
        </center>
    </center>
</body>
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