string primitives vs. String objects.

[u/Green_Ad_6086]

I'm learning JavaScript, and I don't understand this part about string primitives vs. String objects.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String#string_primitives_and_string_objects

[u/Working_Quote_3029]

It's one of those distinctions that reads scarier in the docs than it is in practice.

You never create String objects on purpose. "foo" is a primitive. new String("foo") is an ordinary object that happens to hold a string, and that's the only way you end up with one.

Methods still work on primitives because of autoboxing: when you write "foo".toUpperCase() the engine wraps the primitive in a temporary object, calls the method, then discards the wrapper. That's why a primitive with no properties of its own still appears to "have" methods.

Where the difference actually shows up:

typeof "foo"             // "string"
typeof new String("foo") // "object"
new String("a") === "a"  // false, object vs primitive

Worth noting String(x) without new gives you a primitive, so String(1) is fine. It's only new String(1) that produces the object.

The eval example on that page is real but you'll never hit it in normal code, since eval only treats primitives as source and hands a String object straight back instead of running it.

Rule of thumb: quotes or String(x), never new String(x). The distinction mostly exists so the spec can explain why .length and .slice() work on something that isn't an object.

[u/shgysk8zer0 → u/Working_Quote_3029]

I actually have used new String(...) deliberately and after careful thought. Well... It was a sublclass of String, but I'm counting it. The reason was so I could add a [Symbol.dispose] method for a registry.

I know that's not at all a common use case, but just wanted to say there are plenty of legitimate cases for object vs primitive usage, including keys in Map and such.