This is exactly the problem I've been talking about. A compiler design lecture about implementing a JavaScript engine should not use the term "pass by value" t

This is exactly the problem I've been talking about. A compiler design lecture about implementing a JavaScript engine should not use the term "pass by value" to describe JavaScript's behavior. Most JavaScript engines to date have been written in C/C++. Function parameters are passed by value in these languages, unless you use a reference parameter in C++. This means that if the argument is a struct, the function receives a copy of the struct, not a reference to the original struct that was passed in. Consider this C code: typedef struct { int bar; } Foo; void fun( Foo boo ) { boo.bar = 43; } int main() { Foo foo; foo.bar = 42; printf( "Before call: %d\n", foo.bar ); fun( foo ); printf( "After call: %d\n", foo.bar ); return 0; } This will print: Before call: 42 After call: 42 fun() is passed a copy of the struct, so modifying the struct inside the function only affects its local copy. That's what "pass by value" means in C. Compare with the similar JavaScript: function fun( boo ) { boo.bar = 43; } function main() { let foo = { bar: 42 } console.log( "Before call:", foo.bar ); fun( foo ); console.log( "After call:", foo.bar ); } main(); This will log: Before call: 42 After call: 43 The function doesn't receive a copy of the object, it receives the object itself, under a new name. Using the term "pass by value" for JavaScript's behavior would only invite confusion.