Question 3 "Value Types and Reference Types" is wrong, meaningless, and misleading

[finalchild]

There is no such thing called "value type" or "reference type" in JavaScript. The distinction doesn't exist, not in the spec nor in the implementation. The distinction is a common myth, but factually wrong. JavaScript is not Java.

One does not simply pass strings by value. Strings are not a "non-reference type". Strings are "primitive" in the sense that they don't constitute of properties. This has nothing to do with value and reference.

TL;DR: Almost all types of values in JavaScript are stored as references, and passed by sharing. The small set of exceptions are implementation-specific.

For reference, a nice answer written by jmrk: https://stackoverflow.com/questions/74004695/how-v8-handle-stack-allocated-variable-in-closure

primitive values & object values

• Every value is either a primitive or an object. The terms are defined in the ECMAScript spec.
• Every primitive value is immutable.

storing values

• Some primitive types (string, bigint) don't have a fixed size, despite many referenced articles claiming otherwise.
• Dynamically-sized primitives cannot be stored directly (not by reference. like, in the stack).
• In most JS implementations, some (in V8, most) fixed-size primitives are not stored directly.
• In V8, the only values that are stored directly (situation-specific optimizations aside) are small integer(Smi)s.

passing parameters

• From the perspective of semantics, call-by-value and call-by-sharing have no difference regarding primitive values, since they are immutable. (Except symbols, which should be passed by sharing to carry identity. See "comparing values" below)
• Thus, no special semantics are defined for passing primitives as parameters.
• Most JS implementations don't pass primitives by value. (situation-specific optimizations aside.) Passing strings or bigints by value would incur a significant performance cost. Most implementations don't even pass fixed-size primitives by value.

comparing values

• Objects have "identity", which means that values with same content can be compared different. (think Object.is)
• Symbols, which are primitive, also have identity. https://tc39.es/ecma262/#sec-identity

I suggest that we change the question to something sensible and remove most existing articles. What should the new question be about? Busting this common myth?

[finalchild]

I understand that this repository is mostly stale and stable, but are there any active maintainer who can help resolve this issue? Once the way we handle this is decided, I can work on a PR.

[andrea924breaux]

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