Validating Strings as Alphanumeric Using Regex in JavaScript

2025-04-27 2025-04-27

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To validate alphanumeric characters using regular expressions, use ^[a-zA-Z0-9]+$. This regular expression matches strings composed of one or more alphanumeric characters, such as "3DModel".

If you want to specify a fixed length of alphanumeric characters, use ^[a-zA-Z0-9]{n}$. For example, to match exactly 6 characters, use ^[a-zA-Z0-9]{6}$. Similarly, you can create flexible patterns by specifying minimum and maximum lengths. For instance, ^[a-zA-Z0-9]{12,20}$ is effective for matching strings between 12 and 20 characters.

Below is a summary of commonly used regular expression patterns. Feel free to use them as needed.

#	Match Condition	Regular Expression Pattern
1	Contains only alphanumeric characters	^[a-zA-Z0-9]+$
2	Fixed length of n alphanumeric characters	^[a-zA-Z0-9]{n}$
3	At least n alphanumeric characters	^[a-zA-Z0-9]{n,}$
4	No more than m alphanumeric characters	^[a-zA-Z0-9]{1,m}$
5	Between n and m alphanumeric characters	^[a-zA-Z0-9]{n,m}$

A list of common regular expression patterns for validating alphanumeric

Source Code

Below is a JavaScript function to validate if a given string consists only of alphanumeric characters. The function allows validation based on the following conditions:

If the minimum length is omitted: Validates that the string is within the specified maximum length and consists only of alphanumeric characters.
If the maximum length is omitted: Validates that the string meets the minimum length requirement and consists only of alphanumeric characters.
If both minimum and maximum lengths are omitted: Validates that the string entirely consists of alphanumeric characters.

/**
 * Checks whether a given string consists only of alphanumeric characters.
 *
 * This function verifies that the string is composed of alphanumeric characters
 * and that its length falls within the specified range.
 *
 * @param {string} str The input string.
 * @param {?number} minLength The minimum number of characters (treated as 1 if null).
 * @param {?number} maxLength The maximum number of characters (treated as the length of the string if null).
 * @return {boolean} Returns true if the input string meets the conditions; otherwise, returns false.
 * @throws {Error} Throws an error if the minimum length is less than 1,
 * or if the maximum length is less than the minimum length.
 */
function isAlphanumeric(str, minLength = null, maxLength = null) {
    // Set default values
    const min = minLength === null ? 1 : Number(minLength);
    const max = maxLength === null ? str.length : Number(maxLength);

    // Type checks for input values
    if (isNaN(min)) {
        throw new Error("The minimum length must be an integer.");
    }

    if (isNaN(max)) {
        throw new Error("The maximum length must be an integer.");
    }

    // Validate arguments
    if (min < 1) {
        // Throw an error if the minimum length is less than 1
        throw new Error("The minimum length must be an integer greater than or equal to 1.");
    }

    if (maxLength !== null && max < min) {
        // Throw an error if the maximum length is less than the minimum length
        throw new Error("The minimum length must not exceed the maximum length.");
    }

    // Construct the regular expression pattern for alphanumeric characters and symbols
    const pattern = maxLength === null
        ? new RegExp(`^[a-zA-Z0-9]{${min},}$`) // No limit on the maximum number of characters
        : new RegExp(`^[a-zA-Z0-9]{${min},${max}}$`);

    // Perform the validation using regular expressions
    return pattern.test(str);
}