JavaScript to find Power of a number without using pow() function

To find the Power of a number in JavaScript you can use the readily available function Math.pow().

But sometimes, especially in the interviews they might ask you to write a simple JavaScript program to calculate the power of a number without using the JavaScript pow() function.

Here is a small example of “Power of a number”

5² = 5 * 5, value is 25

Here in the above expression example, 5 is the base & 2 is the exponent

Another example, 5³ = 5 * 5 * 5, value is 125

So basically we need get two values from the user, base & exponent then to find the power, just loop exponent times and multiple the base value.

Let’s write a custom JavaScript function to find the power of a number:

function PowerOfNumber(b,e){
  
  var i, pow = 1;

  //loop exponent times
  for(i=0; i<e; i++){
    //multiple the base value
    pow = pow*b;
  }

  return pow;
}

b and e is the base and exponent in the above function

Let’s write a HTML example to see the output:

<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8" />
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title>Javascript to find power of a number</title>
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <!-- Load Bootstrap library for better UI look & feel -->
  <link rel="stylesheet" type="text/css" media="screen" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css"
  />
  <script>
    function calcPower() {

      //get the value of base & power
      var b = document.getElementById("pow").value;
      var e = document.getElementById("exp").value;
      var res; 

      res = PowerOfNumber(b,e);      
      document.getElementById("res").innerHTML = res;
    }

    function PowerOfNumber(b,e){
      
      var i, pow = 1;

      //loop exponent times
      for(i=0; i<e; i++){
        //multiple the base value
        pow = pow*b;
      }

      return pow;
    }
  </script>
</head>

<body>
  <div class="container">
    <br />
    <h2>Javascript to find Power of a number without using pow()</h2>
    <br />
    <div class="row">
      <div class="col-lg-4">
        <div class="input-group mb-4">
          <input type="number" class="form-control" id="pow" placeholder="Base" min="1">
          <div class="input-group-prepend">
            <span class="input-group-text">-</span>
          </div>
          <input type="number" class="form-control" id="exp" placeholder="Exponent" min="1">
          <button type="submit" class="btn btn-primary" onclick="calcPower()">Submit</button>
        </div>
        <div>Result: <span id="res"></span>
          <div>
          </div>
        </div>
      </div>
    </div>
</body>

</html>

See the demo of this above script here: