Run results for: string[index] vs charAt(index) vs charCodeAt(index)

Test name	Executions per second
✓ String[index]	486,514 Ops/sec
String.charAt(index)	375,268 Ops/sec
String.charCodeAt(index)	58,410 Ops/sec

Script Preparation code:

const PERIOD = '.';
const SINGLE_QUOTE = "'";
const DOUBLE_QUOTE = '"';
const BACK_TICK = '`';

function getPartsWithStringIndex(text) {
    const parts = [];
    let path;
    let partStart = 0;
    let partEnd = -1;
    let quotedWith = null;
    let previous;
    let current;
    for (let index = 0; index <= text.length; index++) {
        previous = current;
        current = text[index];

        if (index === partStart) {
            if (current === DOUBLE_QUOTE || current === SINGLE_QUOTE || current === BACK_TICK) {
                quotedWith = current;
                continue;
            }
        }
        if (typeof current === 'undefined' ||
            (current === PERIOD && (!quotedWith || previous === quotedWith))) {
            partEnd = index;
        }
        if (partStart < partEnd) {
            if (quotedWith) {
                path = text.substring(partStart + 1, index - 1);
                quotedWith = null;
            } else {
                path = text.substring(partStart, index);
            }
            parts.push({
                path
            });
            partStart = index + 1;
        }
    }

    return parts;
}

function getPartsWithCharAt(text) {
    const parts = [];
    let path;
    let partStart = 0;
    let partEnd = -1;
    let quotedWith = null;
    let previous;
    let current;
    for (let index = 0; index <= text.length; index++) {
        previous = current;
        current = text.charAt(index);

        if (index === partStart) {
            if (current === DOUBLE_QUOTE || current === SINGLE_QUOTE || current === BACK_TICK) {
                quotedWith = current;
                continue;
            }
        }
        if (current === '' ||
            (current === PERIOD && (!quotedWith || previous === quotedWith))) {
            partEnd = index;
        }
        if (partStart < partEnd) {
            if (quotedWith) {
                path = text.substring(partStart + 1, index - 1);
                quotedWith = null;
            } else {
                path = text.substring(partStart, index);
            }
            parts.push({
                path
            });
            partStart = index + 1;
        }
    }

    return parts;
}
const PERIOD_CODE = '.'.charCodeAt(0);
const SINGLE_QUOTE_CODE = "'".charCodeAt(0);
const DOUBLE_QUOTE_CODE = '"'.charCodeAt(0);
const BACK_TICK_CODE = '`'.charCodeAt(0);

function getPartsWithCharCodeAt(text) {
    const parts = [];
    let path;
    let partStart = 0;
    let partEnd = -1;
    let quotedWith = null;
    let previous;
    let current;
    for (let index = 0; index <= text.length; index++) {
        previous = current;
        current = text.charCodeAt(index);

        if (index === partStart) {
            if (current === DOUBLE_QUOTE_CODE ||
                current === SINGLE_QUOTE_CODE ||
                current === BACK_TICK_CODE) {
                quotedWith = current;
                continue;
            }
        }
        if (isNaN(current) || (current === PERIOD_CODE && (!quotedWith || previous === quotedWith))) {
            partEnd = index;
        }
        if (partStart < partEnd) {
            if (quotedWith) {
                path = text.substring(partStart + 1, index - 1);
                quotedWith = null;
            } else {
                path = text.substring(partStart, index);
            }
            parts.push({
                path
            });
            partStart = index + 1;
        }
    }

    return parts;
}
var testCases = [
    // subset of cases
    'path.to.a.value',
    'pathTo.someSpecified.aValue',
    'path."with `inner` quoted"."`parts`"',
    'path."with spaces"."to a value"',
    'path."with.dots"."to.a.value"'
]
var partsCount = 0

Tests:

String[index]
partsCount = 0 for (const testCase of testCases) { const parts = getPartsWithStringIndex(testCase) partsCount += parts.length } if (partsCount !== 16) throw new Error('String[index] invalid parts count ' + partsCount)
String.charAt(index)
partsCount = 0 for (const testCase of testCases) { const parts = getPartsWithCharAt(testCase) partsCount += parts.length } if (partsCount !== 16) throw new Error('String[index] invalid parts count ' + partsCount)
String.charCodeAt(index)
partsCount = 0 for (const testCase of testCases) { const parts = getPartsWithCharCodeAt(testCase) partsCount += parts.length } if (partsCount !== 16) throw new Error('String[index] invalid parts count ' + partsCount)

Run results for: string[index] vs charAt(index) vs charCodeAt(index)

Compare same algorithm using javascript String[index] vs String.charAt(index) vs String.charCodeAt(index)

String[index]

String.charAt(index)

String.charCodeAt(index)