How to check integer value in JavaScript - onlyxcodes

## Wednesday 19 July 2023

You will learn how to check integer values in JavaScript or determine whether a variable is an integer in this article.

We occasionally need to add integer numbers that users enter into the input text box of our web application on the client side.

When users send data in string format, we must verify whether the values are integers or not.

This post gives a solution and demonstrates how to use JavaScript to verify if the supplied values are integers.

## check integer value in JavaScript

JavaScript provides several techniques for determining whether a value is an integer.Â

Here are a few different methods for doing so:

Using the Number.isInteger() method:

The Number.isInteger() method analyzes whether or not a given number is an integer. If the value is an integer, it returns true; if not, it returns false.

``````<html>
<title>Check integer value in JavaScript</title>
<body>
<script type="text/javascript">

const value = 42;
if (Number.isInteger(value))
{
console.log("The value is an integer.");
}
else
{
console.log("The value is not an integer.");
}
</script>
</body>
</html>

``````

Using the modulo operator %:

The remainder of a division operation is returned by the modulo operator. If a number is an integer, dividing it by one leaves a zero-valued residue.

``````<html>
<title>Check integer value in JavaScript</title>
<body>
<script type="text/javascript">

const value = 42;
if (value % 1 === 0)
{
console.log("The value is an integer.");
}
else
{
console.log("The value is not an integer.");
}

</script>
</body>
</html>

``````

Using parseInt() and comparing with the original value:

A string is parsed using the parseInt() function, which then returns an integer. The value is an integer if the parsed integer equals the original value as a number.

``````<html>
<title>Check integer value in JavaScript</title>
<body>
<script type="text/javascript">

const value = "42";
if (parseInt(value) === Number(value))
{
console.log("The value is an integer.");
}
else
{
console.log("The value is not an integer.");
}

</script>
</body>
</html>

``````

Due to JavaScript's flexible typing, values occasionally appearing to be integers may actually be of a different type (such as a textual representation of a number).Â

The safest and most dependable way to check integer values in JavaScript is to use Number.isInteger().

## How to check if a string is an integer in JavaScript?

Any information that is displayed to the user must include a string. There are numerous techniques available in JavaScript for altering strings.Â

Numerical values have occasionally also been perceived as strings. It is preferable in this situation to determine whether the variable or value is a number or string. JavaScript provides a number of techniques for doing this.

This lesson will show you how to use a variety of JavaScript methods to determine whether a string is an integer.

Here are a few notable methods:

Using parseInt():

JavaScript's parseInt() method makes an effort to transform a string into an integer.Â

It will return the integer value if the string represents an actual integer; else, it will return NaN (Not a Number).

``````<html>
<title>check if a string is an integer in JavaScript</title>
<body>
<script type="text/javascript">

function isInteger(str)
{
return !isNaN(parseInt(str)) && Number.isInteger(parseFloat(str));
}

// Example usage:
console.log(isInteger("123")); // Output: true
console.log(isInteger("-42")); // Output: true
console.log(isInteger("3.14")); // Output: false
console.log(isInteger("abc")); // Output: false

</script>
</body>
</html>
``````

Using a Regular Expression:

If the string just contains digits, you can check it using a regular expression, with or without an optional sign at the beginning.

``````<html>
<title>check if a string is an integer in JavaScript</title>
<body>
<script type="text/javascript">

function isInteger(str)
{
return /^\s*(\+|-)?\d+\s*\$/.test(str);
}

// Example usage:
console.log(isInteger("123")); // Output: true
console.log(isInteger("-42")); // Output: true
console.log(isInteger("3.14")); // Output: false
console.log(isInteger("abc")); // Output: false

</script>
</body>
</html>
``````

You can detect whether or not a given string represents an integer using each of the two techniques.Â

The first approach is more adaptable because it supports leading and trailing spaces in addition to the (+/-) symbol.Â

The second approach is stronger and looks for an exact integer digit match. Select the one that best meets your needs.

## How to check if an integer is positive or negative in JavaScript?

In JavaScript, there are two easy ways to determine whether a given number is positive or negative.Â

Here, the first approach makes use of JavaScript conditional statements, and the second approach makes use of a new ES6 function named Math.sign().

Using Conditional Statements:

You may use a simple conditional statement in JavaScript to determine whether a number is positive or negative. Here is how to go about it:

``````<html>
<title> check if an integer is positive or negative in JavaScript?</title>
<body>
<script type="text/javascript">

function checkPositiveOrNegative(number)
{
if (number > 0)
{
console.log("The integer is positive.");

}
else if (number < 0)
{
console.log("The integer is negative.");
}
else
{
console.log("The integer is zero.");
}
}

checkPositiveOrNegative(5); // Output: "The integer is positive."
checkPositiveOrNegative(-3); // Output: "The integer is negative."
checkPositiveOrNegative(0); // Output: "The integer is zero."

</script>
</body>
</html>
``````

TheÂ checkPositiveOrNegativeÂ function, which accepts an integer as its inputÂ (number), is defined in this code. To determine the value of the integer, we utilize an if-else statement inside the function:

If a number is greater than 0, we print "The integer is positive."

If a number is less than 0, we print "The integer is negative."

If a number is exactly 0, we print "The integer is zero."

Any number can be used as an argument when calling this function, and it will return true, false, or zero depending on the value.Â

For instance:

``````checkPositiveOrNegative(5); // Output: "The integer is positive."
checkPositiveOrNegative(-3); // Output: "The integer is negative."
checkPositiveOrNegative(0); // Output: "The integer is zero."``````

Using Math.sign():

JavaScript includes a function called Math. sign() that can be used to determine a number's sign, or whether it is positive or negative.Â

Parameters:Â The number that you want to know the sign of is represented by the single parameter number that this function accepts. Return Value: The Math +/- 1, which denotes the sign of the argument-passed number.

A +/- 0 is returned if the value supplied to Math.sign() is 0. It should be noted that an explicit (+) will not be returned if the number is positive.

In this example, I checked the output of the Math.sign() function for a specified amount using the JavaScript Ternary (conditional) Operator.

Output:

``13 is positive``

Check the return type as well.

``````<html>
<title> check if an integer is positive or negative in JavaScript?</title>
<body>
<script type="text/javascript">

const number = 13;
document.write (Math.sign(number));

</script>
</body>
</html>
``````

Output:

``1``

You should see the positive number 1, which is the output.

That is a simple way to tell whether an integer in JavaScript is positive or negative.

## How to check input is a number in JavaScript?

In our client-side web application, there are instances where the user must fill out one or more HTML form fields with numbers (0â€“9), such as when entering a phone number and zip code.Â

JavaScript scripts can be written to perform numerous operations, such as determining whether an input is a number. Here are some methods:

Using isNaN() function:

The "is Not a Number" (isNaN) function returns true if the supplied value is not a number and returns false otherwise.

``````<html>
<title>check input is a number in JavaScript</title>
<body>
<script type="text/javascript">

function isNumber(input)
{

return !isNaN(input);
}

// Example usage:
console.log(isNumber(42)); // Output: true
console.log(isNumber("Hello")); // Output: false
console.log(isNumber("123")); // Output: true (it is considered a number)

</script>
</body>
</html>
``````

Using typeof operator:

TheÂ typeofÂ operator returns a string that encapsulates the variable's data type. It can be used to determine whether the input is a number.

``````<html>
<title>check input is a number in JavaScript</title>
<body>
<script type="text/javascript">

function isNumber(input)
{
return typeof input === 'number';
}

// Example usage:
console.log(isNumber(42)); // Output: true
console.log(isNumber("Hello")); // Output: false
console.log(isNumber("123")); // Output: false

</script>
</body>
</html>
``````

Using Regular Expression:

If the input is a number, you can check it with a regular expression. This method is more adaptable since it enables the validation of several number formats (such as integers and floating-point numbers).

``````<html>
<title>check input is a number in JavaScript</title>
<body>
<script type="text/javascript">

function isNumber(input)
{

return /^-?\d+(\.\d+)?\$/.test(input);
}

// Example usage:
console.log(isNumber(42)); // Output: true
console.log(isNumber("123")); // Output: true
console.log(isNumber("3.14")); // Output: true
console.log(isNumber("-42")); // Output: true
console.log(isNumber("Hello")); // Output: false

</script>
</body>
</html>
``````

Select the approach based on your individual requirements. The first approach (isNaN()) might be a preferable choice if you simply want to take into account strictly numeric values without allowing strings that contain numbers.Â

The regular expression approach, on the other hand, offers more versatility for handling various number formats.

## How to check if a number is a float or int in JavaScript?

Due to the loosely typing of JavaScript, all data types are stored in a single format variable. The variable is transferable to any other type.

We need to explicitly check the type of variables in several situations. For instance, if the current variable contains a number, we must ascertain whether it is an integer or a float value.

To determine whether a number is a float or an int, we'll write a function, use the Number.isInteger() method, and apply the modulo operator.

Using the Number.isInteger() method:

The Number.isInteger() method determines whether or not a given number is an integer (a whole number). If the input is an integer, it returns true; if a float or nothing at all, it returns false.

``````<html>
<title>check if a number is a float or int in JavaScript</title>
<body>
<script type="text/javascript">

function checkNumberType(number)
{
if (Number.isInteger(number))
{
console.log(number + " is an integer.");
}
else
{
console.log(number + " is a float.");
}
}

// Examples:
checkNumberType(5); // Output: 5 is an integer.
checkNumberType(3.14); // Output: 3.14 is a float.
checkNumberType(10.0); // Output: 10 is an integer.
checkNumberType(0.5); // Output: 0.5 is a float.

</script>
</body>
</html>
``````

Using the modulo operator (%):

When two numbers are split, the modulo operator determines the remainder. A number is an integer if the remainder is 0, otherwise, it is a float.

``````<html>
<title>check if a number is a float or int in JavaScript</title>
<body>
<script type="text/javascript">

function checkNumberType(number)
{
if (number % 1 === 0)
{
console.log(number + " is an integer.");
}
else
{
console.log(number + " is a float.");
}
}

// Examples:
checkNumberType(5); // Output: 5 is an integer.
checkNumberType(3.14); // Output: 3.14 is a float.
checkNumberType(10.0); // Output: 10 is an integer.
checkNumberType(0.5); // Output: 0.5 is a float.

</script>
</body>
</html>
``````

For the majority of practical applications, both techniques will yield the same answer, but using Number.isInteger() is generally thought to be more accurate and reliable, especially when working with huge numbers or advanced instances.

## How to find if a number is an integer or decimal in JavaScript?

JavaScript's modulo operator (%) and simple comparisons can be used to detect whether a number is an integer or a decimal. A decimal number has a decimal portion, but an integer is a whole number without one.

A function to determine whether a given number is an integer or a decimal is provided below:

``````<html>
<title>find if a number is an integer or decimal in JavaScript</title>
<body>
<script type="text/javascript">

function isIntegerOrDecimal(number)
{
// Check if the number is a valid numeric value

if (typeof number !== 'number' || isNaN(number))
{
return false;

}

// Check if the number is an integer (whole number)

if (number % 1 === 0)
{
return "integer";
}
else
{
return "decimal";
}
}

// Example usage:
console.log(isIntegerOrDecimal(5)); // Output: "integer"
console.log(isIntegerOrDecimal(3.14)); // Output: "decimal"
console.log(isIntegerOrDecimal(0.25)); // Output: "decimal"
console.log(isIntegerOrDecimal(-10)); // Output: "integer"
console.log(isIntegerOrDecimal("hello")); // Output: false (not a number)

</script>
</body>
</html>
``````

TheÂ typeofÂ andÂ isNaNÂ functions in the function first determine whether the input is a valid numeric number.Â

The modulo operatorÂ %Â is then used to determine whether or not the integer contains a tiny part. The number is an integer if the remainder is zero; else, it is a decimal.Â

Accordingly, "integer" or "decimal" is returned by the function. It returns false if the input is not a valid number.