I’m reading the MDN web docs on globalThis.
It says:
Note: The globalThis property is configurable and writable so that
code authors can hide it when executing untrusted code and prevent
exposing the global object.
I want to do exactly this, creating a sandbox of sorts so that a function can be written which accesses variables in the sandbox without needing to prefix it with anything and also preventing any variables not in the sandbox object from being accessible – like an improved alternative to the deprecated “with” construct which will fail to find anything not in the global context I define.
I wrote a proof of concept running in an ES6 module:
let myContext = { a:1, b:2 }
let f = ()=> {
let savedGlobal = globalThis
globalThis = myContext
let ret = a+b
savedGlobal.globalThis = savedGlobal
return ret
}
f()
As an explanation, I am first saving the current value of globalThis to a local variable, as I expect that otherwise the original value won’t be accessible from my new global context. Then I hide the existing global context by overwriting it with my own, which the documentation seems to suggest is possible. Then I try to assign a local variable to the result of a+b which should be 1+2 = 3, then I restore the global context from the local saved value and return the value I calculated.
If I log the variables, I see that globalThis is the Window object before I assign to it, and it’s myContext after, but I still get a reference error “a is not defined” despite the fact that I would expect that it would find it in the now global context “myContext”. It also successfully ran the console.log despite the fact that I would expect it to no longer be visible after reassigning globalThis.
6
As commented in your question, you will not be able to customize the javascript identifier resolution process…
You can make your own workaround like this:
function F ()
{
return this.a + this.b;
}
var a = 5;
var b = 6;
// Unbound
console.log(F());
// Outputs 11, because this is globalThis in browsers (undefined in Node).
// Bound to context A
console.log(F.apply({a: 1, b: 2}));
// Outputs 3, because the this inside the function is replaced with the object above.
// ...
// Bound to context N
console.log(F.apply({a: 3, b: 4}));
// Outputs 7, because the this inside the function is replaced with the object above.I hope this helps solving your problem.