Why every execution context has Realm?

Question

I'm reading ECMAScript 2023. It say all execution contexts has "Realm" state component.

And it describes,

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.

I understand realm is for global environment like window(browser), global(node). And I understand "Global Environment Records" already define global environment once on first code evaluation.

I wonder why a Realm for a execution context is needed.

I'm reading https://tc39.es/ecma262/#sec-execution-contexts.

Answer 1

You can find the current Realm record as "the value of the Realm component of the running execution context".

That term is referenced multiple times across the specification, mostly for bookkeeping to carry-over the value, but in the end to lookup intrinsic prototypes or cached template strings from the current realm.