[2023 Day 3 (Part 1)] [JS] I'm missing something but my head hurts.

2023day3part1.js

var fs = require("fs");

try {
    var data = fs.readFileSync("day3input.txt", "utf8");
} catch (e) {
    console.log("Error:", e.stack);
}

const separatedLines = data.split(/\r?\n/);
separatedLines.pop();

const reg = /[^.\d]/;

const parts = [];
const symbols = [];

let ans = 0;

separatedLines.map((line, i) => {
    line.split("").map((char, j) => {
        let isSymbol = reg.test(char);

        if (isSymbol) {
            symbols.push(char);
            checkForNums({ x: j, y: i });
        }
    });
});

function checkForNums(symbol) {
    for (let i = -1; i <= 1; i++) {
        for (let j = -1; j <= 1; j++) {
            let x = symbol.x + j;
            let y = symbol.y + i;
            let cell = separatedLines[y] ? separatedLines[y][x] : null ? separatedLines[y][x] : null;

            if (isNum(cell)) {
                let prev = isNum(separatedLines[y][x - 1]);
                let next = isNum(separatedLines[y][x + 1]);

                // .......
                // .145...
                // ...*...
                // ...123.
                //

                if (j === -1 && !next) {
                    parts.push(getNumLeft({ x, y }));
                }

                if (j === 0) {
                    if (prev && !next) {
                        parts.push(getNumLeft({ x, y }));
                    }
                    if (prev && next) {
                        parts.push(getNumMiddle({ x, y }));
                    }
                    if (!prev && next) {
                        parts.push(getNumRight({ x, y }));
                    }
                }

                if (j === 1 && !prev) {
                    parts.push(getNumRight({ x, y }));
                }

                // if solo number
                /* if (!prev && !next) {
                    parts.push(cell);
                } */
            }
        }
    }
}

function isNum(char) {
    return parseInt(char) >= 0;
}

function getNumMiddle(cell) {
    let y = cell.y;
    let xL = cell.x;
    let xR = cell.x + 1;
    let num = [];

    while (isNum(separatedLines[y][xL])) {
        num.unshift(separatedLines[y][xL]);
        xL -= 1;
    }

    while (isNum(separatedLines[y][xR])) {
        num.push(separatedLines[y][xR]);
        xR += 1;
    }

    return num.join("");
}

function getNumLeft(cell) {
    let y = cell.y;
    let x = cell.x;
    let num = [];

    while (isNum(separatedLines[y][x])) {
        num.unshift(separatedLines[y][x]);
        x -= 1;
    }

    return num.join("");
}

function getNumRight(cell) {
    let y = cell.y;
    let x = cell.x;
    let num = [];

    while (isNum(separatedLines[y][x])) {
        num.push(separatedLines[y][x]);
        x += 1;
    }

    return num.join("");
}

parts.map((num) => {
    fs.appendFile("day3output.txt", num + "\n", (err) => {
        if (err) console.log(err);
    });
    ans += parseInt(num);
});

console.log(ans);