functionDef.exists()

Signature

exists() => Boolean

Description

Tests if an UDF, represented as an Function document, exists. Fauna stores UDFs as documents in the Function system collection.

Function documents are FQL versions of a database’s FSL function schema. Function documents have the FunctionDef type. See User-defined functions (UDFs).

Staged schema

If a database has staged schema, this method interacts with the database’s staged schema, not the active schema.

exists() vs. null comparisons

You can use either exists() or a null comparison (== null or != null) to check the existence or validity of a value. For example:

Function.byName("createOrUpdateCartItem").exists() // true

Function.byName("createOrUpdateCartItem") != null  // true

Key differences:

  • exists() returns an error if called on an unsupported value.

  • Null comparisons do not throw errors and work safely on any value.

For example:

// Declare an object. Objects don't support
// an `exists()` method.
let object = { a: "Foo", b: "Bar" }

object.exists()  // Returns `invalid_query` error

object != null   // Returns true

Parameters

None

Return value

Type Description

Boolean

If true, the Function document exists. If false, the Function document doesn’t exist.

Examples

Function.byName("checkout").exists()
true
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