query_builder.js

function buildQuery(sql, fields) {

    // get all the fields needed in the where clause
    let field_names = Object.keys(fields);

    // check if a where clause is needed
    if (field_names.length > 0) {
        sql += ' where ' 
    }

    // get all the fields for the where clause with $ placeholder
    let query_fields = field_names.map((field, index) => {
        return field + ' = $' + (index + 1);
    })

    // join fields with an and
    sql += query_fields.join( " and " );

    // get all the parameter values
    let params = field_names.map((field_name) => fields[field_name] );

    return {
        sql,
        params
    }
}

let queryData = buildQuery('select * from shoes', {
    brand_id: 17,
    size_id: 12,
    // color_id: 47 
});

// pool.query(queryData.sql, queryData.params);

console.log(queryData);