change global function scope in javascript

Question

Is the following possible:

var someObject = {someProperty : "someValue"};
var someFunction = function() {
 someProperty = "anotherValue";
};

// what do I do here, in order to use
// someFunction to change someObject,
// without altering either of those things?

// directly accessing "someObject" in someFunction
// is not an option. e.g., none of this:
/*
   var someFunction = function() {
       someObject.someProperty = "anotherValue";
   };
*/

if(someObject.someProperty=="anotherValue") alert("Hooray!");

?

If not in regular JavaScript, is this possible in Mozilla's JavaScript for Firefox extensions?

Thanks.

Answer 1

No you can't.

var someFunction = function() {
    someProperty = "anotherValue";
};

Here someProperty is a global variable (created if not accessed before).

var someObject = {someProperty : "someValue"};

Here someProperty is a key of an object (not a variable).

So in each context the token someProperty refers to something different and completely independent.

There is no way for the function to alter the value of the object without a direct reference / calling another function to do it.

Answer 2

eval("someObject.someProperty='anotherValue'");

Will that work? What do you consider "directly accessing "someObject" in someFunction?" You're going to have to access someObject somehow if you want to change its property...

Answer 3

If you are prepared to modify your function to reference this.someProperty instead of just someProperty, then you can use the apply or call:

var someFunction = function() {
  this.someProperty = "anotherValue";
};

someFunction.apply(someObject);

Answer 4

No. This is all about scoping (environments) and properties.

When you say someObject = ... or someobject.whatever what you are saying is give me the someObject in the nearest scope and then do something with it.

Scopes nest. Functions create a new scope and capture the surrounding scope. Variables in closer scopes can shadow variables in surrounding scopes. Your function can see everything in the scope it was declared in, so it can see someObject.

someProperty is part of a key/value pair in someObject. Nothing cat get to it without going through someObject and asking it to retreive the value stored with the key someProperty.

Answer 5

For purely academic purpose, here's a way:

with (someObject) {
  eval('(' +someFunction.toString() + ')();');
}

Don't use this in production environment!

[Edit]: Just to clarify, here's how you use it.

var someObject = {someProperty : "someValue"};
var someFunction = function() {
 someProperty = "anotherValue";
};

with (someObject) {
  eval('(' +someFunction.toString() + ')();');
}

if(someObject.someProperty=="anotherValue") alert("Hooray!");

It DOES NOT refer to someObject inside someFunction.

Answer 6

For those who may be wondering, the closest thing I've found is Components.utils.evalInSandbox. It's definitely not perfect, but easily the best thing for this problem.

Answer 7

var someObject = {someProperty : "someValue"};
with (someObject)
{
  window.someFunction = function() {
   someProperty = "anotherValue";
  };
}

if(someObject.someProperty=="anotherValue") alert("Hooray!");

Not the best coding practice but should perform what you want.