Sorry, how do you unfreeze a frozen object? Only references I see online involve cloning it, which preserves the security properties of a frozen object. As for

Sorry, how do you unfreeze a frozen object? Only references I see online involve cloning it, which preserves the security properties of a frozen object. As for harden(), whether its vulnerable to it's prototype chain in the way you describe depends entirely on how it's written. That said, these aren't amateurs so I expect they know what they're doing, and transitively freezing an object graph does add important security properties.