JavaScript UDF Limitations¶

Maximum Size of JavaScript Source Code¶

Snowflake limits the maximum size of the JavaScript source code in the body of a JavaScript UDF. Snowflake recommends limiting the size to 100 KB. (The code is stored in a compressed form, and the exact limit depends on the compressibility of the code.)

Consuming Too Much Memory Will Cause UDF to Fail¶

JavaScript UDFs will fail if they consume too much memory. The specific limit is subject to change. Using too much memory will result in an error being returned.

Taking Too Long to Complete Will Cause a UDF to Be Killed and an Error Returned¶

JavaScript UDFs that take too long to complete will be killed and an error returned to the user. In addition, JavaScript UDFs that enter endless loops will result in errors.

Excess Stack Depth Will Result in an Error¶

Excessive stack depth due to recursion will result in an error.

Global State¶

Snowflake usually preserves the JavaScript global state between iterations of a UDF. However, you should not rely on previous modifications to the global state being available between function calls. Additionally, you should not assume that all rows will execute within the same JavaScript environment.

In practice, the global state is relevant with:

• Complex/expensive initialization logic. By default, the provided UDF code is evaluated for every row processed. If that code contains complex logic, this might be inefficient.

• Functions that contain code that is not idempotent. A typical pattern would be:

  Date.prototype._originalToString = Date.prototype.toString;
  Date.prototype.toString = function() {
    /* ... SOME CUSTOM CODE ... */
    this._originalToString()
    }
  

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  The first time that this code is executed, it changes the state of toString and _originalToString. Those changes are preserved in the global state, and the second time that this code is executed, the values are changed again in a way that creates recursion. The second time that toString is called, the code recurses infinitely (until it runs out of stack space).

For these situations, a recommended pattern is to guarantee that relevant code is evaluated only once, using JavaScript’s global variable semantics. For example:

var setup = function() {
/* SETUP LOGIC */
};

if (typeof(setup_done) === "undefined") {
  setup();
  setup_done = true;  // setting global variable to true
}

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Note that this mechanism is only safe for caching the effects of code evaluation. It is not guaranteed that after an initialization the global context will be preserved for all rows, and no business logic should depend on it.

JavaScript Libraries¶

JavaScript UDFs support access to the standard JavaScript library. Note that this excludes many objects and methods typically provided by browsers. There is no mechanism to import, include, or call additional libraries. All required code should be embedded within the UDF.

Additionally, the built-in JavaScript eval() function is disabled.

Returned Variant Size and Depth¶

Returned variant objects are subject to size and nesting-depth limitations:

Size:

Currently limited to several megabytes, but subject to change.

Depth:

Currently limited to a nesting depth of 1000, but subject to change.

If any object is too large or too deep, an error is returned when the UDF is called.

Argument and Return Type Constraints Are Sometimes Ignored¶

Certain type characteristics declared for an argument or return value will be ignored when the UDF is called. In these cases, the received value may be used as received whether or not it conforms to constraints specified in the declaration.

The following are ignored for UDFs whose logic is written in JavaScript:

• Length for arguments of type VARCHAR

CREATE OR REPLACE FUNCTION tf (arg1 VARCHAR(1))
RETURNS VARCHAR(1)
LANGUAGE JAVASCRIPT AS 'return A.substr(3, 3);';