Identifying False values in JavaScript

JavascriptWeb DevelopmentObject Oriented Programming

JavaScript has the following values evaluate to false when evaluated as Boolean type − false

  • 0
  • empty string: "" , '' , or ``
  • null
  • undefined
  • NaN — not a number value

Following is the code for identifying falsy values in JavaScript −

Example

 Live Demo

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
<style>
   body {
      font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
   }
   .result{
      font-size: 20px;
      font-weight: 500;
      color: blueviolet;
   }
</style>
</head>
<body>
<h1>Identifying Falsy values in JavaScript.</h1>
<div class="result"></div>
<br />
<button class="Btn">CLICK HERE</button>
<h3>Click on the above button to identify some of the falsy values in JavaScript</h3>
<script>
   let resEle = document.querySelector(".result");
   let BtnEle = document.querySelector(".Btn");
   BtnEle.addEventListener("click", () => {
      if(!0){
         resEle.innerHTML = '0 evaluates to boolean false <br>';
      }
      if(!''){
         resEle.innerHTML += " '' evaluates to boolean false <br>";
      }
      if(!null){
         resEle.innerHTML += 'null evaluates to boolean false <br>';
      }
      if(!undefined){
         resEle.innerHTML += 'undefined evaluates to boolean false <br>';
      }
      if(!NaN){
         resEle.innerHTML += 'Nan evaluates to boolean false <br>';
      }
   });
</script>
</body>
</html>

Output

On clicking the ‘CLICK HERE’ button −

raja
Published on 22-Jul-2020 07:50:15
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