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Changing the Primitive-String a String-Object References

Ignoring all best practices, I have a rather academic question that I'll ask for curiosity's sake.

As you know, you can add custom properties to a string Object:

var s = new String("initial string");
var s.customProperty = "Please Don't Forget about me";

Is it possible (without creating a new string object), to change the string-primitive that "s" references?

Specifically, I want to change "s" (above), so that s == "new string", yet after making this change, I want s.customProperty to still point to the string-primitive: "Please Don't Forget about me". Again, I want to achieve this without having to create any new string objects.

var s = new String("initial string");
var s.customProperty = "Please Don't Forget about me";

// What code must preceed the following "if statement" in order
// for it to return "true" (giving the restrictions I described
// in the paragraphs of this post)?

if(s == "new string" && s.customProperty == "Please Don't Forget about me")
{
    console.log("true");
}
else
{
    console.log("false");
}

In other words, is possible to change a string object's reference-pointer without losing or cloning all custom properties that have been added to that string object?

Solution

  • Is it possible to change the string-primitive that a "s" references?

    No. The [[StringData]] (ES6) / [[PrimitiveValue]] (ES5) it contains is an internal slot and cannot be mutated.

    … without having to create any new string objects.

    There's no way around that.

    What you possibly can do is to subclass String and overwrite all methods to refer to a mutable property, but that advice is as good as "don't use String objects". See also the answers to the inverse problem Is there a way to Object.freeze() a JavaScript Date?.