JavaScript large string concat benchmark (v8 + NodeJS)

stringConcatBench.js

#!/usr/bin/env node

const { Buffer } = require('node:buffer');

function main() {
    console.log(`NodeJS version = ${process.versions.node}`);
    console.log(`V8 version     = ${process.versions.v8}`);
    console.log("---------------------------------------------------")
    measureStringConcat();
}

function measureStringConcat() {
    for (const strLen of [
        1,      // Probably 1-2 words in memory
        8,      // Probably 2 or more words in memory on (on 64-bit)
        32,     // Probably fits in a single L1 cache line
        3072,   // <4096 -> Probably fits into a single page
        2*4096, // >4096 -> Probably fits into multiple pages
    ]) {
        const RAND_STRS_N      = 256;
        const RAND_STRS_STRIDE = 13;
        const placeholderStr = "\x00".repeat(strLen);
        const randStrs = Array(RAND_STRS_N).fill(placeholderStr);
        for (let i = 0; i < RAND_STRS_N; i++) {
            let randStr = "";
            for (let j = 0; j < strLen; j++) {
                const randCharCode = Math.floor(Math.random()*127.99999);
                randStr += String.fromCharCode(randCharCode);
            }
            randStrs[i] = randStr;
        }

        console.log(`concatenating strings with ${strLen} characters`);
        let randStrIdx = 0;
        for (const [strsN, reps] of [
            [   100, 100_000],
            [ 1_000,  10_000],
            [10_000,    1000],
        ]) {
            console.log(`    no. of strings = ${strsN}`)
            console.log(`    no. of reps    = ${reps}`)
            {
                const timeLabel = "        string concat with '+='                ";
                console.time(timeLabel)
                for (let i = 0; i < reps; i++) {
                    let strAgg = "";
                    for (let j = 0; j < strsN; j++) {
                        strAgg += randStrs[randStrIdx];

                        randStrIdx += RAND_STRS_STRIDE;
                        if (randStrIdx > RAND_STRS_N) randStrIdx -= RAND_STRS_STRIDE;
                    }
                }
                console.timeEnd(timeLabel);
            }
            {
                const timeLabel = "        string concat with '.concat'           ";
                console.time(timeLabel)
                for (let i = 0; i < reps; i++) {
                    let strAgg = "";
                    for (let j = 0; j < strsN; j++) {
                        strAgg = strAgg.concat(randStrs[randStrIdx]);

                        randStrIdx += RAND_STRS_STRIDE;
                        if (randStrIdx > RAND_STRS_N) randStrIdx -= RAND_STRS_STRIDE;
                    }
                }
                console.timeEnd(timeLabel);
            }
            {
                const timeLabel = "        string concat with 'template literals' ";
                console.time(timeLabel)
                for (let i = 0; i < reps; i++) {
                    let strAgg = "";
                    for (let j = 0; j < strsN; j++) {
                        strAgg = `${strAgg}${randStrs[randStrIdx]}`;

                        randStrIdx += RAND_STRS_STRIDE;
                        if (randStrIdx > RAND_STRS_N) randStrIdx -= RAND_STRS_STRIDE;
                    }
                }
                console.timeEnd(timeLabel);
            }
            {
                const timeLabel = "        string concat with 'array join'        ";
                console.time(timeLabel)
                for (let i = 0; i < reps; i++) {
                    const l = [];
                    for (let j = 0; j < strsN; j++) {
                        l.push(randStrs[randStrIdx]);

                        randStrIdx += RAND_STRS_STRIDE;
                        if (randStrIdx > RAND_STRS_N) randStrIdx -= RAND_STRS_STRIDE;
                    }
                    const strAgg = l.join("");
                }
                console.timeEnd(timeLabel);
            }
            {
                const timeLabel = "        string concat with 'array reduce'      ";
                console.time(timeLabel)
                for (let i = 0; i < reps; i++) {
                    const l = [];
                    for (let j = 0; j < strsN; j++) {
                        l.push(randStrs[randStrIdx]);

                        randStrIdx += RAND_STRS_STRIDE;
                        if (randStrIdx > RAND_STRS_N) randStrIdx -= RAND_STRS_STRIDE;
                    }
                    const strAgg = l.reduce((agg, s) => agg + s, "");
                }
                console.timeEnd(timeLabel);
            }
            {
                const timeLabel = "        string concat by 'writing to buffer'   ";
                console.time(timeLabel)
                for (let i = 0; i < reps; i++) {
                    const buf = Buffer.allocUnsafe(strLen*strsN);
                    let   bufOffset = 0;
                    for (let j = 0; j < strsN; j++) {
                        buf.write(randStrs[randStrIdx], bufOffset);
                        bufOffset += strLen;

                        randStrIdx += RAND_STRS_STRIDE;
                        if (randStrIdx > RAND_STRS_N) randStrIdx -= RAND_STRS_STRIDE;
                    }
                    const strAgg = buf.toString();
                }
                console.timeEnd(timeLabel);
            }
        }
    }
}

main();