How to check if string contains only digits in JavaScript ?

Checking if a string contains only digits in JavaScript involves verifying that every character in the string is a numerical digit (0-9).

Examples of checking if string contains only digits in JavaScript

1. Using Regular Expression

Regular expressions (regex) are patterns used to match character combinations in strings. In JavaScript, they are typically defined between forward slashes /, like /pattern/. To check if a string contains only digits, you can use the regex pattern ^\d+$.

Example: The containsOnlyDigits function uses a regular expression (/^\d+$/) to test if a string consists only of digits. It returns true if the string matches the pattern (only digits), and false otherwise.

JavaScript

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

console.log(containsOnlyDigits("123")); // Output: true
console.log(containsOnlyDigits("123abc")); // Output: false

Output

true
false

2. Using isNaN() Function

The isNaN() function in JavaScript checks if a value is “Not-a-Number” (NaN). By converting a string to a number using parseFloat(), it can determine if the string contains only digits. If the conversion is successful, it returns false, indicating that the string contains only digits. Otherwise, it returns true.

Example: The containsOnlyDigits function checks if a string contains only digits by attempting to convert it to a number using parseFloat(). It returns true if successful, indicating the string contains only digits, otherwise false.

JavaScript

function containsOnlyDigits(str) {
  return !isNaN(str) && !isNaN(parseFloat(str));
}

console.log(containsOnlyDigits("123")); // Output: true
console.log(containsOnlyDigits("123abc")); // Output: false

Output

true
false