Simple database that packs records into contiguous memory

db.js

const POOL_SIZE = 4 * 1024;
let mySchema = ['int32', 'char(32)', 'int32'];

let bufferPool = new ArrayBuffer(POOL_SIZE);
let dir = {
    tbl: {
        people: { offset: 0, size: 0 }
    }
};

function colSize(col) {
    if (col === 'int32') {
        return 4;
    }
    if (col.startsWith('char')) {
        let [ _, chars ] = col.match(/char\((\d+)\)/);
        return parseInt(chars);
    }
    return 0;
}

function rowSize(schema) {
    let size = 0;
    for (const col of schema) {
        size += colSize(col);
    }
    
    return size;
}

function readRow(tblOffset, rowOffset, schema) {
    let out = [];
    const rs = rowSize(schema);
    let rowView = new DataView(bufferPool, tblOffset + rowOffset * rs, rs);
    for (let i = 0, colOffset = 0; i < schema.length; i++) {
        const col = schema[i];
        const cs = colSize(col);
        if (col === 'int32') {
            out.push(rowView.getInt32(colOffset));
        } else if (col.startsWith('char')) {
            let chars = new Array(cs);
            for (let j = 0; j < cs; j++) {
                let byte = rowView.getUint8(colOffset + j);
                if (byte === 0) {
                    break;
                }
                chars[j] = String.fromCharCode(byte);
            }
            out.push(chars.join(''));
        }
        colOffset += cs;
    }
    
    return out;
}

function writeRow(tblOffset, rowOffset, schema, row) {
    const rs = rowSize(schema);
    let rowView = new DataView(bufferPool, tblOffset + rowOffset * rs, rs);
    if (schema.length !== row.length) {
        throw new Error('Row length does not match schema length');
    }
    for (let i = 0, colOffset = 0; i < schema.length; i++) {
        const col = schema[i];
        const val = row[i];
        const cs = colSize(col);
        if (col === 'int32') {
            rowView.setInt32(colOffset, val);
        } else if (col.startsWith('char')) {
            // Could the rest of the col buffer be uninitialized?
            for (let j = 0; j < val.length; j++) {
                rowView.setUint8(colOffset + j, val.charCodeAt(j));
            }
        }
        colOffset += cs;
    }
}

const tblOffset = dir.tbl.people.offset;
writeRow(tblOffset, 0, mySchema, [1, 'Andrew', 28]);
writeRow(tblOffset, 1, mySchema, [2, 'Diana', 31]);
writeRow(tblOffset, 2, mySchema, [3, 'Audrey', 6]);
writeRow(tblOffset, 3, mySchema, [4, 'Jonah', 4]);
writeRow(tblOffset, 4, mySchema, [5, 'Abel', 3]);

// console.log(new Uint8Array(bufferPool));
console.log(readRow(tblOffset, 4, mySchema));