CharAt

A Node.js string may contain many characters. We can iterate over these characters with a for-loop, and then index the characters or use charAt.

With the result from charAt, we can access other arrays and objects. This helps us develop complex algorithms and thus improve performance.

CharAt example

The charAt function takes a 1-character string at an index. It is the same as the string indexer in functionality.

var letters = "abc";

// Loop over all string indexes.
for (var i = 0; i < letters.length; i++) {
    // Use charAt to get a 1-char string.
    var result = letters.charAt(i);
    // The letter is a string that is 1 char long.
    console.log("LETTER: " + result);
    console.log("LETTER LENGTH: " + result.length);
}
LETTER: a
LETTER LENGTH: 1
LETTER: b
LETTER LENGTH: 1
LETTER: c
LETTER LENGTH: 1

CharCodeAt

This function converts a character at an index into its ASCII (or Unicode) equivalent int. It does not handle all Unicode values. But it can handle ASCII strings well.

var letters = "abc";

for (var i = 0; i < letters.length; i++) {
    // Use charCodeAt to get ASCII values from letters.
    var point = letters.charCodeAt(i);
    console.log("CHARCODEAT: " + point);
}
CHARCODEAT: 97
CHARCODEAT: 98
CHARCODEAT: 99

String.fromCharCode

With charCodeAt we get a character code from a string. And with String.fromCharCode we convert a character code back into a string.

var input = "c";

// Get char code and reduce it by one.
var letterCode = input.charCodeAt(0);
letterCode--;

// Convert char code into a string.
var result = String.fromCharCode(letterCode);

// Display the values.
console.log("INPUT: " + input);
console.log("CHARCODEAT: " + letterCode);
console.log("FROMCHARCODE: " + result);
console.log("LENGTH: " + result.length);
INPUT: c
CHARCODEAT: 98
FROMCHARCODE: b
LENGTH: 1

CharCodeAt, scan string

With charCodeAt we can test a string for multiple values in a single pass. This can avoid excessive loops over a string with indexOf.

function hasParentheses(value) {
    for (var i = 0; i < value.length; i++) {
        var code = value.charCodeAt(i);
        switch (code) {
            case 40: // Left parenthesis.
            case 41: // Right parenthesis.
                return true;
        }
    }
    return false;
}

if (hasParentheses("cat(dog)")) {
    console.log(true);
}
if (!hasParentheses("bird")) {
    console.log(true);
}
true
true

With charAt, we can optimize certain string-processing algorithms. We can avoid copying strings repeatedly as multiple transformations are applied.