Explain JavaScript eval() function what are the rules to be followed while using it.

The eval() function is used to evaluate the given string and execute it as JavaScript code. Using eval() is highly dangerous as someone can pass malicious code as input string to one of out inputs.

Following is the code to show eval() function in JavaScript −


 Live Demo

<!DOCTYPE html>
<html lang="en">
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
   body {
      font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
   .result {
      font-size: 20px;
      font-weight: 500;
<h1>JavaScript eval() function</h1>
<div style="color: green;" class="result"></div>
<button class="Btn">CLICK HERE</button>
<h3>Click on the above button to see eval() usage</h3>
   let resEle = document.querySelector(".result");
   let BtnEle = document.querySelector(".Btn");
   function multiply(a, b) {
      return a * b;
   BtnEle.addEventListener("click", () => {
      resEle.innerHTML += eval("12+92") + "";
      eval('resEle.innerHTML += "Hello world "');
      resEle.innerHTML += eval("multiply(12,33)");


The above code will produce the following output −

On clicking the ‘CLICK HERE’ button −

Updated on: 18-Jul-2020


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