April 6, 2022

How to Check if String is Integer or Float in Javascript

By Krishnaa JavaScript Questions 0 Comments

In this tutorial, you will learn how to check if string is integer or float in javascript. In a floating number, the whole number part is separated from the fractional part using a decimal point or dot (.). 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. The point to be noted here is that only a round number or whole number is considered to be a valid integer.

There are numerous ways to check if a string is an integer or float. We are going to use one of the easiest solutions which involve the usage of the match() method, parseFloat() method, isInteger() method, and ternary (?) operator. The ternary operator is also known as the conditional operator which acts similar to the if-else statement.

The match() methods matches a string against a regular expression. If the match is found, it returns an array of matches, otherwise returns null. The parseFloat() method takes a string as a parameter and returns a floating-point number.

The isInteger() methods checks whether a variable is an integer or not. The parseInt() method takes a string as a parameter and returns an integer based upon the specified radix.

In the following example, we have one global variable and upon click of a button, we will check if the string is an integer or float 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, 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">
<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 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 string as its value.
We have attached a click event listener to the button element.
In the event handler function, we are calling getNumType() method and passing myVar as a parameter. This method will check if the string is an integer or float.
In the getNumType() method, we are calling isFloat() and isInteger() methods one by one. Both methods return a boolean value. Depending upon those boolean values, we are returning "Float", "Integer" or "Unknown".
In the isFloat(), we are using match() method, parseFloat() method, isInteger() method and ternary (?) operator to verify whether myVar is float or not.
In the isInteger(), we are using match() method, parseInt() method, and isInteger() method to verify whether myVar is an integer or not.
We are assigning the returned value from getNumType() method 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 = "5.6";

btnCheck.addEventListener("click", () => {
  let result = getNumType(myVar);
  output.innerText = result;
});

function getNumType(str) {
  if (isFloat(str)) return "Float";
  if (isInteger(str)) return "Integer";
  return "Unknown";
}

function isFloat(str) {
  let pattern = /^-?\d*(\.\d+)?$/;
  if (!str.match(pattern)) return false;
  let val = parseFloat(str);
  const isInteger = Number.isInteger(val);
  return isInteger ? false : true;
}

function isInteger(str) {
  let pattern = /^-?[0-9]+$/;
  if (!str.match(pattern)) return false;
  let val = parseInt(str);
  const isInteger = Number.isInteger(val);
  return isInteger;
}

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