Short-circuit evaluation in JavaScript

Javascript Web Development Object Oriented Programming

Short circuit evaluation basically works with the && and || logical operators. The expressions are evaluated left to right.

For && operator − Short circuit evaluation with &&(AND) logical operator means if the first expression evaluates to false then whole expression will be false and the rest of the expressions will not be evaluated.

For || operator − Short circuit evaluation with ||(OR) logical operator means if the first expression evaluates to true then the whole expression will be true and the rest of the expressions will not be evaluated.

Following is the code for short circuit evaluation 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>Short-circuit evaluation</h1>
<div class="result"></div>
<br />
<button class="Btn">&& short circuit evaluation</button>
<button class="Btn">|| short circuit evaluation</button>
<h3>Click on the above button to see the the short circuit evaluation</h3>
<script>
   let resEle = document.querySelector(".result");
   let BtnEle = document.querySelectorAll(".Btn");
   function retTrue() {
      resEle.innerHTML += "True <br>";
      return true;
   }
   function retFalse() {
      resEle.innerHTML += "False <br>";
      return false;
   }
   BtnEle[0].addEventListener("click", () => {
      resEle.innerHTML = "&& evaluation<br>";
      retFalse() && retTrue();
   });
   BtnEle[1].addEventListener("click", () => {
      resEle.innerHTML = "|| evaluation <br>";
      retTrue() || retFalse();
   });
</script>
</body>
</html>

Output

On clicking the “&& short circuit evaluation” button −

On clicking the ‘|| short circuit evaluation” button −

AmitDiwan

Updated on 18-Jul-2020 08:08:40

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