How to Check if Variable is Negative in Javascript

In this tutorial, you will learn how to check if variable is negative in javascript. There is no dedicated data type that represents integer in javascript. All the numbers or numeric values are of number type. Since we have integer type in various other programming languages, we mistakenly refer numeric values as integer type in javascript.

An integer is considered to be negative integer if the value is less than 0.

There are numerous ways to check if a variable is negative. We are going to use one of the easiest solutions which involve the usage of the isInteger() method and ternary (?) operator.  The isInteger() methods checks whether a variable is an integer or not. The ternary operator is also known as the conditional operator which acts similar to the if-else statement.

In the following example, we have one global variable and upon click of a button, we will check if the variable is negative and display the result on the screen.  Please have a look over the code example and the steps given below.


  • We have 3 elements in the HTML file (div, button, and h1). The div element is just a wrapper for the rest of the elements.
  • The innerText for the button element is “Check” and for the h1 element, it is “Result”.
  • We have done some basic styling using CSS and added the link to our style.css stylesheet inside the head element.
  • We have also included our javascript file script.js with a script tag at the bottom.
<!DOCTYPE html>
<html lang="en">
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <link rel="stylesheet" href="style.css">

    <script src="script.js"></script>
body {
    text-align: center;

div {
    display: inline-block;

button {
    display: inline-block;
    padding: 10px 20px;


  • We have selected the button element and h1 element using the document.querySelector() method and stored them in btnCheck and output variables respectively.
  • We have a global variable myVar which holds a number as its value.
  • We have attached a click event listener to the button element.
  • In the event handler function, we are using isInteger()method  and ternary (?) operator to verify whether myVar is negative or not. Depending upon the result of the check, we will assign “Yes” or “No” to the result variable
  • We are displaying the result in the h1 element using the innerText property.
let btnCheck = document.querySelector("button");
let output = document.querySelector("h1");

let myVar = -100;

btnCheck.addEventListener("click", () => {
  output.innerText = Number.isInteger(myVar) && myVar < 0 ? "Yes" : "No";