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JavaScript string is number check | Example code

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Use the isNaN() method to check the string number in JavaScript. This works regardless of whether the variable content is a string or number.

isNaN(num)

The isNaN() function determines whether the given value is a number or an illegal number (Not-a-Number). It returns true if the variable does NOT contain a valid number.

Check if a string contains only digits.

let isnum = /^\d+$/.test(val);

Check if the JavaScript string is a number

Simple example code.

<!DOCTYPE html>
<html>
<body>
  <script>

    console.log("Valid num",isNaN('195'))
    console.log("Valid num",isNaN('boo'))
    console.log("Valid num",isNaN('100px'))

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

Output:

JavaScript string is number check

Creating a function that negates the output of the isNaN() function.

function isNum(val){
  return !isNaN(val)
}
console.log(isNum('ABC'));          
console.log(isNum('12345'));        
console.log(isNum('-1'));

Output:

false
true
true

Using Regular Expression

You can also use regular expressions to check if a string contains only numeric characters.

function isStringNumber(str) {
    return /^\d+$/.test(str);
}

console.log(isStringNumber("123")); // true
console.log(isStringNumber("abc")); // false

Using Unary Plus Operator

Another method is to use the unary plus operator (+) to attempt to convert the string into a number. If the conversion is successful, it’s a number; otherwise, it’s not.

function isStringNumber(str) {
    return !isNaN(+str);
}

console.log(isStringNumber("123")); // true
console.log(isStringNumber("abc")); // false

Choose the method that best fits your requirements and coding style.

Comment if you have any doubts or suggestions on this JS string topic.

Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.

OS: Windows 10

Code: HTML 5 Version

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