js_lang stored procedure and function overview

This feature is a tech preview. Before using this feature in production, we recommend that you test restoring production from physical backups in your environment, and also use the alternative backup method for redundancy.

You can use stored procedures and functions written in JS with a MySQL-compatible database. This feature helps you manage complex data processing tasks. This method improves performance. This method lets developers run complex operations faster. If you know JS, you can use your existing skills. Using stored procedures and functions reduces the work done by client applications. Using stored procedures and functions also improves overall system performance. Using stored procedures and functions helps developers process data faster. Using stored procedures and functions also makes maintenance and scaling easier. This approach is a good solution for developers who know JS.

Benefit	Description
Familiarity	Developers who already know JS can use their existing skills.
Efficiency	JS can run complex data processing tasks more efficiently.
Performance	Stored procedures and functions in JS improve database performance. They reduce the work done by client applications.
Reusability	You can write code once in stored procedures and functions. Then you can use that code in multiple applications.
Scalability	Using stored procedures and functions makes database operations easier to maintain and scale.
Simplified Development Process	This feature makes development easier for developers who know JS.
Integration with Client Applications	Stored procedures and functions work well with client applications. You need less additional processing.
Optimization	This feature improves overall system performance through efficient data processing.

Limitations

The JS procedure parameters cannot be JS reserved words and must be legal JS identifiers.

Our implementation offers the same level of JS support as the V8 engine inside the context of a database engine. You can check out the details at v8.dev/docs and tc39.es/ecma262. Developers have access to standard operators, data types, objects (such as Math), and functions defined in the ECMAScript standard. However, objects and modules specific to Node.NS or DOM, which are only available in browsers, are not accessible.

In a typical database environment, direct access to external files (like reading or writing files on the server’s file system) is restricted. Our implementation adheres to a trusted external routine language policy, ensuring routines cannot perform operations beyond what is normally possible for database users. Consequently, file or network I/O operations are not supported within our routines.

Our system supports asynchronous JS code, but it does not work well for database routines. Since everything runs on the same thread and there is nothing to wait for asynchronously, using asynchronous code is unnecessary and not recommended.

We always run JS code in strict mode, and developers cannot disable or change this setting.

Convert SQL data types to JS

SQL and JS use different data types, so our implementation converts values when passing SQL parameters to JS and back. The following rules explain how these conversions work:

SQL NULL values are converted to JS null values.

SQL type	JS return type	Notes
BOOLEAN, TINYINT, SHORTINT, MEDIUMINT, INT	Number
BIGINT	Number or BigInt	Number for values [-2^53-1, 2^53-1], BigInt otherwise
DECIMAL	String
FLOAT, DOUBLE	Number
BIT(k)	Number or BigInt	Number for k ≤ 53, BigInt for k > 53
TIME, DATE, TIMESTAMP, DATETIME	String
YEAR	Number
CHAR, VARCHAR, TINYTEXT, TEXT, MEDIUMTEXT, LONGTEXT	String	Fails if length exceeds 2^29 - 24
BINARY, VARBINARY, TINYBLOB, BLOB, MEDIUMBLOB, LONGBLOB	DataView
ENUM, SET	String
GEOMETRY and spatial types	DataView
JSON	Object

When the data converts to a JS string, it automatically changes from the SQL parameter’s character set to utf8mb4, which JS uses.

Convert JS data types to SQL

The system uses the target SQL data type to determine how to convert each value. It typically converts a JS value into a basic type—such as a string, integer, or double—based on the specified SQL type. Once converted, the system stores the result in the corresponding SQL parameter or return value.

If a value exceeds allowed limits or uses an unsupported format, the conversion fails and triggers an error. During this process, the system automatically converts JS strings from the utf8mb4 encoding to the character set defined by the SQL parameter.

The system always maps JS null and undefined values to SQL NULL, regardless of the target SQL type.

JS to SQL type conversion rules

Target SQL Data Type	Conversion Rules	Explanation	Example
BOOLEAN, TINYINT, SHORTINT, MEDIUMINT, INT, BIGINT	(Version 8.4.5) - Numbers: stored as integers - Booleans: true → 1, false → 0 - BigInts: stored as integers when possible - Other types: converted to strings first (Version 8.4.4) - JS Integers/Numbers: integers stored as-is, BigInts attempted as integers, others as strings.)	Preserves native numeric forms where possible; other values default to string representation	42 → 42 3.14 → "3.14" true → "1"
DECIMAL	- All values converted to strings - Booleans: converted to 0/1, then stored as doubles	Supports precision formatting; special handling ensures Booleans fit numeric context	123.45 → "123.45" true → 1.0
FLOAT, DOUBLE	- Numbers: stored as doubles - (Version 8.4.5) - Booleans: converted to 0/1, then stored as doubles - Others: converted to strings	Treats numeric and Boolean inputs consistently using floating-point representation	3.14 → 3.14 true → 1.0 "3.14" → "3.14"
BIT	Converted to SQL BIT type	Only binary-compatible values allowed	1 → BIT(1)
TIME, DATE, TIMESTAMP, DATETIME	All values converted to strings	Usually expects ISO date formats or equivalents	Date() → "2024-01-30"
CHAR, VARCHAR, TEXT, etc.	All values converted to strings Charset conversion from utf8mb4 if needed	Supports text types with encoding fallback	"hello" → "hello"
BINARY, VARBINARY, BLOB, etc.	- ArrayBuffer/View: stored directly - Others: converted to strings	Binary data must be explicitly wrapped; others fallback to string	buffer → binary
SET	- Numbers: stored as integers/doubles - BigInts: stored as integers - Others: converted to strings with charset conversion if needed	Tries native storage before falling back to strings	1 → 1 "value" → "value"
GEOMETRY	- Valid ArrayBuffer/View: stored as binary - Others: cause an error	Enforces format rules to maintain spatial integrity	valid buffer → GEOMETRY
JSON	Converted using JSON.stringify()	Converts objects or arrays to serialized strings	{key: "value"} → "{"key":"value"}"

Further reading

• Install js_lang component
• Uninstall the js_lang component
• js_lang stored function or procedure
• js_lang privileges
• Troubleshoot js_lang procedures and functions