Check if a JavaScript string contains only alpha or alphanumeric characters
![](/assets/cover/mountain-lake-cottage-2-800.webp)
Oftentimes, strings are used to represent data that should only contain alphabetic or alphanumeric characters. Using regular expressions, you can easily check if a string matches the pattern.
Check if a string contains only alpha characters
For alpha (alphabetic) characters, you can use a range ([a-zA-Z]
) to match any character from a
to z
(lowercase) and A
to Z
(uppercase). Simply adding the *
quantifier and the positional anchors (^
and $
) will ensure that the pattern matches the entire string. Then, you can use RegExp.prototype.test()
to check if the given string matches against the alphabetic pattern.
const isAlpha = str => /^[a-zA-Z]*$/.test(str); isAlpha('sampleInput'); // true isAlpha('this Will fail'); // false isAlpha('123'); // false
Check if a string contains only alphanumeric characters
Subsequently, you can extend the pattern to include digits (0-9
) by adding them to the range. The resulting pattern will be [a-zA-Z0-9]
. Adding the gi
flags makes the pattern case-insensitive, allowing for the range to be simplified to [a-z0-9]
.
const isAlphaNumeric = str => /^[a-z0-9]*$/gi.test(str); isAlphaNumeric('hello123'); // true isAlphaNumeric('123'); // true isAlphaNumeric('hello 123'); // false (space character is not alphanumeric) isAlphaNumeric('#$hello'); // false
These methods can serve as a great starting point for more complex string validation patterns. You can further customize the regular expressions to suit your specific requirements (e.g. allowing spaces, hyphens, or underscores in the string).