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.
HTML & CSS
- We have 3 elements in the HTML file (
div
,button
, andh1
). Thediv
element is just a wrapper for the rest of the elements. - The
innerText
for thebutton
element is“Check”
and for theh1
element, it is“Result”
. - We have done some basic styling using CSS and added the link to our
style.css
stylesheet inside thehead
element. - We have also included our javascript file
script.js
with ascript
tag at the bottom.
<!DOCTYPE html> <html lang="en"> <head> <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"> <title>Document</title> </head> <body> <div> <button>Check</button> <h1>Result</h1> </div> <script src="script.js"></script> </body> </html>
body { text-align: center; } div { display: inline-block; } button { display: inline-block; padding: 10px 20px; }
Javascript
- We have selected the
button
element andh1
element using thedocument.querySelector()
method and stored them inbtnCheck
andoutput
variables respectively. - We have a global variable
myVar
which holds a number as its value. - We have attached a
click
event listener to thebutton
element. - In the event handler function, we are using
isInteger()
method and ternary (?
) operator to verify whethermyVar
is negative or not. Depending upon the result of the check, we will assign“Yes”
or“No”
to theresult
variable - We are displaying the
result
in theh1
element using theinnerText
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"; });