ECMAScript® 2024 Language Specification

Draft ECMA-262 / February 15, 2024

9.3 Realms

Before it is evaluated, all ECMAScript code must be associated with a realm. Conceptually, a realm consists of a set of intrinsic objects, an ECMAScript global environment, all of the ECMAScript code that is loaded within the scope of that global environment, and other associated state and resources.

A realm is represented in this specification as a Realm Record with the fields specified in Table 24:

Table 24: Realm Record Fields
Field Name Value Meaning
[[AgentSignifier]] an agent signifier The agent that owns this realm
[[Intrinsics]] a Record whose field names are intrinsic keys and whose values are objects The intrinsic values used by code associated with this realm
[[GlobalObject]] an Object or undefined The global object for this realm
[[GlobalEnv]] a Global Environment Record The global environment for this realm
[[TemplateMap]] a List of Records with fields [[Site]] (a TemplateLiteral Parse Node) and [[Array]] (an Array)

Template objects are canonicalized separately for each realm using its Realm Record's [[TemplateMap]]. Each [[Site]] value is a Parse Node that is a TemplateLiteral. The associated [[Array]] value is the corresponding template object that is passed to a tag function.

Note 1
Once a Parse Node becomes unreachable, the corresponding [[Array]] is also unreachable, and it would be unobservable if an implementation removed the pair from the [[TemplateMap]] list.
[[LoadedModules]] a List of Records with fields [[Specifier]] (a String) and [[Module]] (a Module Record)

A map from the specifier strings imported by this realm to the resolved Module Record. The list does not contain two different Records with the same [[Specifier]].

Note 2
As mentioned in HostLoadImportedModule ( Note 1), [[LoadedModules]] in Realm Records is only used when running an import() expression in a context where there is no active script or module.
[[HostDefined]] anything (default value is undefined) Field reserved for use by hosts that need to associate additional information with a Realm Record.

9.3.1 CreateRealm ( )

The abstract operation CreateRealm takes no arguments and returns a Realm Record. It performs the following steps when called:

  1. Let realmRec be a new Realm Record.
  2. Perform CreateIntrinsics(realmRec).
  3. Set realmRec.[[AgentSignifier]] to AgentSignifier().
  4. Set realmRec.[[GlobalObject]] to undefined.
  5. Set realmRec.[[GlobalEnv]] to undefined.
  6. Set realmRec.[[TemplateMap]] to a new empty List.
  7. Return realmRec.

9.3.2 CreateIntrinsics ( realmRec )

The abstract operation CreateIntrinsics takes argument realmRec (a Realm Record) and returns unused. It performs the following steps when called:

  1. Set realmRec.[[Intrinsics]] to a new Record.
  2. Set fields of realmRec.[[Intrinsics]] with the values listed in Table 6. The field names are the names listed in column one of the table. The value of each field is a new object value fully and recursively populated with property values as defined by the specification of each object in clauses 19 through 28. All object property values are newly created object values. All values that are built-in function objects are created by performing CreateBuiltinFunction(steps, length, name, slots, realmRec, prototype) where steps is the definition of that function provided by this specification, name is the initial value of the function's "name" property, length is the initial value of the function's "length" property, slots is a list of the names, if any, of the function's specified internal slots, and prototype is the specified value of the function's [[Prototype]] internal slot. The creation of the intrinsics and their properties must be ordered to avoid any dependencies upon objects that have not yet been created.
  3. Perform AddRestrictedFunctionProperties(realmRec.[[Intrinsics]].[[%Function.prototype%]], realmRec).
  4. Return unused.

9.3.3 SetRealmGlobalObject ( realmRec, globalObj, thisValue )

The abstract operation SetRealmGlobalObject takes arguments realmRec (a Realm Record), globalObj (an Object or undefined), and thisValue (an Object or undefined) and returns unused. It performs the following steps when called:

  1. If globalObj is undefined, then
    1. Let intrinsics be realmRec.[[Intrinsics]].
    2. Set globalObj to OrdinaryObjectCreate(intrinsics.[[%Object.prototype%]]).
  2. Assert: globalObj is an Object.
  3. If thisValue is undefined, set thisValue to globalObj.
  4. Set realmRec.[[GlobalObject]] to globalObj.
  5. Let newGlobalEnv be NewGlobalEnvironment(globalObj, thisValue).
  6. Set realmRec.[[GlobalEnv]] to newGlobalEnv.
  7. Return unused.

9.3.4 SetDefaultGlobalBindings ( realmRec )

The abstract operation SetDefaultGlobalBindings takes argument realmRec (a Realm Record) and returns either a normal completion containing an Object or a throw completion. It performs the following steps when called:

  1. Let global be realmRec.[[GlobalObject]].
  2. For each property of the Global Object specified in clause 19, do
    1. Let name be the String value of the property name.
    2. Let desc be the fully populated data Property Descriptor for the property, containing the specified attributes for the property. For properties listed in 19.2, 19.3, or 19.4 the value of the [[Value]] attribute is the corresponding intrinsic object from realmRec.
    3. Perform ? DefinePropertyOrThrow(global, name, desc).
  3. Return global.