The charCodeAt() method retrieves the 16-bit Unicode code unit value for a character at a specified index in a string. Character classification can be performed by checking which of the following standard Unicode ranges the code unit falls into:

1. Uppercase Latin letters (A-Z): 65 to 90
2. Lowercase Latin letters (a-z): 97 to 122
3. Arabic numerals (0-9): 48 to 57
4. Common simplified Chinese characters: 19968 (U+4E00) to 40869 (U+9FA5)

The code snippet below prints each character in a sample string alongside its corresponding code unit:

var sampleText:String = "greeting! 世界你好! 42!";
for (var index:int = 0; index < sampleText.length; index++) {
    trace(sampleText.charAt(index), " | ", sampleText.charCodeAt(index));
}

Character and Code Unit Conversion

Convert character to Unicode code unit

Syntax: stringVariable.charCodeAt(positionIndex)

var testChar:String = "B";
trace(testChar.charCodeAt(0)); // Output: 66

Convert Unicode code unit to character

Syntax: String.fromCharCode(codeUnitValue)

var convertedChar:String = String.fromCharCode(122);
trace(convertedChar); // Output: z

Method 1: Per-Character Iteration Validation

This approach traverses every character in the input string and checks if it falls with in the allowed Unicode ranges:

/**
 * Validates if all characters in input are Chinese, Latin letters, or digits
 * @param inputStr String to validate
 * @return True if all characters meet requirements, false otherwise
 */
public function checkValidCharSet(inputStr:String):Boolean {
    for (var pos:int = 0; pos < inputStr.length; pos++) {
        var charCode:Number = inputStr.charCodeAt(pos);
        const isChinese:Boolean = charCode >= 19968 && charCode <= 40869;
        const isDigit:Boolean = charCode >= 48 && charCode <= 57;
        const isUppercaseLetter:Boolean = charCode >= 65 && charCode <= 90;
        const isLowercaseLetter:Boolean = charCode >= 97 && charCode <= 122;
        
        if (!isChinese && !isDigit && !isUppercaseLetter && !isLowercaseLetter) {
            return false;
        }
    }
    return true;
}

Method 2: Regular Expression Validation

This method uses a precompiled regular expression to perform full string validation in a single operation:

/**
 * Validates if all characters in input are Chinese, Latin letters, or digits
 * @param inputStr String to validate
 * @return True if all characters meet requirements, false otherwise
 */
public function validateAlnumChinese(inputStr:String):Boolean {
    var validationRegex:RegExp = /^[a-zA-Z0-9\u4e00-\u9fa5]+$/;
    return validationRegex.test(inputStr);
}