MDTable.js

const defaultOptions = {};

class MDTable {
    #columns = [];
    #columnWidth = new Map();
    #options = {};

    constructor(data, options) {
        this.#options = {
            ...options,
            ...defaultOptions
        };
        this.data = data;

        this.#init();
    }

    toString() {
        return [
            this.#renderHeader(),
            this.#renderHeaderSplit(),
            ...this.data.map((item) => this.#renderRow(item)),
        ].join("\n");
    }

    #init() {
        this.#makeColumns();
        this.#calcColumnWidth();
    }

    #makeColumns() {
        if (this.#options.columns !== undefined) {
            this.#columns = this.#options.columns;
            return;
        }

        const columns = new Set();
        this.data.forEach(i => {
            Object.entries(i).forEach(([key, _]) => {
                columns.add(key);
            })
        })
        this.#columns = [...columns];
    }

    #calcColumnWidth() {
        const result = new Map();

        // Add header to data fot calculate length
        const headerData = {};
        this.#columns.forEach(i => headerData[i] = i);
        const data = [...this.data, headerData];

        data.forEach(i => {
            Object.entries(i).forEach(([key, value]) => {
                const length = String(value ?? "").trim().length
                if (!result.has(key)) {
                    result.set(key, length);
                } else {
                    if ((result.get(key) ?? 0) < length) {
                        result.set(key, length)
                    }
                }
            })
        });

        this.#columnWidth = result;
    }

    #textAsWidth(text, width) {
        if (width === undefined) return text;
        let spaces = width - text.length;
        if (spaces < 0) spaces = 0;
        return text.trim() + " ".repeat(spaces);
    }

    #renderHeader() {
        let header = '| ';

        const last = this.#columns.length;
        this.#columns.forEach((i, index) => {
            const width = this.#columnWidth.get(i);
            header += this.#textAsWidth(i, width);
            header += last === (index + 1) ? " |" : " | ";
        });

        return header;
    }

    #renderHeaderSplit() {
        let header = '|';

        const last = this.#columns.length;
        this.#columns.forEach((i, index) => {
            const width = this.#columnWidth.get(i) ?? 0;
            header += "-".repeat(width + 2) + "|";
        });

        return header;
    }

    #renderRow(item) {
        if (typeof item === 'string') return `| ${item} |`
        let row = '| ';

        const last = this.#columns.length;
        this.#columns.forEach((key, index) => {
            const text = String(item[key] ?? '');
            const width = this.#columnWidth.get(key) ?? 0;
            row += this.#textAsWidth(text, width);
            row += last === (index + 1) ? " |" : " | ";
        });

        return row;
    }
}

module.exports = {
    MDTable
}