JavaScript pass scope to another function

问题

Is it possible to somehow pass the scope of a function to another?

For example,

function a(){
   var x = 5;
   var obj = {..};
   b(<my-scope>);
}

function b(){
   //access x or obj....
}

I would rather access the variables directly, i.e., not using anything like this.a or this.obj, but just use x or obj directly.

回答1:

The only way to truly get access to function a's private scope is to declare b inside of a so it forms a closure that allows implicit access to a's variables.

Here are some options for you.

Direct Access

Declare b inside of a.

function a() {
   var x = 5,
      obj = {};
   function b(){
      // access x or obj...
   }
   b();
}

a();

If you don't want b inside of a, then you could have them both inside a larger container scope:

function container() {
   var x, obj;
   function a(){
      x = 5;
      obj = {..};
      b();
   }
   function b(){
      // access x or obj...
   }
}

container.a();

These are the only ways you're going to be able to use a's variables directly in b without some extra code to move things around. If you are content with a little bit of "help" and/or indirection, here are a few more ideas.

Indirect Access

You can just pass the variables as parameters, but won't have write access except to properties of objects:

function a() {
   var x = 5,
      obj = {};
   b(x, obj);
}

function b(x, obj){
   // access x or obj...
   // changing x here won't change x in a, but you can modify properties of obj
}

a();

As a variation on this you could get write access by passing updated values back to a like so:

// in a:
var ret = b(x, obj);
x = ret.x;
obj = ret.obj;

// in b:
return {x : x, obj : obj};

You could pass b an object with getters and setters that can access a's private variables:

function a(){
   var x = 5,
      obj = {..},
      translator = {
         getX : function() {return x;},
         setX : function(value) {x = value;},
         getObj : function() {return obj;},
         setObj : function(value) {obj = value;}
      };
   b(translator);
}

function b(t){
   var x = t.getX(),
      obj = t.getObj();

   // use x or obj...
   t.setX(x);
   t.setObj(obj);

   // or you can just directly modify obj's properties:
   obj.key = value;
}

a();

The getters and setters could be public, assigned to the this object of a, but this way they are only accessible if explicitly given out from within a.

And you could put your variables in an object and pass the object around:

function a(){
   var v = {
      x : 5,
      obj : {}
   };
   b(v);
}

function b(v){
   // access v.x or v.obj...
   // or set new local x and obj variables to these and use them.
}

a();

As a variation you can construct the object at call time instead:

function a(){
   var x = 5,
      obj = {};
   b({x : x, obj: obj});
}

function b(v){
   // access v.x or v.obj...
   // or set new local x and obj variables to these and use them.
}

a();

回答2:

Scope is created by functions, and a scope stays with a function, so the closest thing to what you're asking will be to pass a function out of a() to b(), and that function will continue to have access to the scoped variables from a().

function a(){
   var x = 5;
   var obj = {..};
   b(function() { /* this can access var x and var obj */ });
}
function b( fn ){

    fn(); // the function passed still has access to the variables from a()

}

While b() doesn't have direct access to the variables that the function passed does, data types where a reference is passed, like an Object, can be accessed if the function passed returns that object.

function a(){
   var x = 5;
   var obj = {..};
   b(function() { x++; return obj; });
}
function b( fn ){

    var obj = fn();
    obj.some_prop = 'some value'; // This new property will be updated in the
                                  //    same obj referenced in a()

}

回答3:

No.

You're accessing the local scope object. The [[Context]].

You cannot publicly access it.

Now since it's node.js you should be able to write a C++ plugin that gives you access to the [[Context]] object. I highly recommend against this as it brings proprietary extensions to the JavaScript language.

回答4:

what about using bind

function funcA(param) {     
    var bscoped = funcB.bind(this);     
    bscoped(param1,param2...)
}

回答5:

As others have said, you cannot pass scope like that. You can however scope variables properly using self executing anonymous functions (or immediately executing if you're pedantic):

(function(){
    var x = 5;
    var obj = {x:x};
    module.a = function(){
        module.b();
    };
    module.b = function(){
        alert(obj.x);    
    };
}());

a();

回答6:

I think the simplest thing you can do is pass variables from one scope to a function outside that scope. If you pass by reference (like Objects), b has 'access' to it (see obj.someprop in the following):

function a(){
   var x = 5;
   var obj = {someprop : 1};
   b(x, obj);
   alert(x); => 5
   alert(obj.someprop); //=> 'otherval'
}
function b(aa,obj){
   x += 1; //won't affect x in function a, because x is passed by value
   obj.someprop = 'otherval'; //change obj in function a, is passed by reference
}

回答7:

You can't "pass the scope"... not that I know of.
You can pass the object that the function is referring to by using apply or call and send the current object (this) as the first parameter instead of just calling the function:

function b(){
    alert(this.x);
}
function a(){
    this.x = 2;
    b.call(this);
}

The only way for a function to access a certain scope is to be declared in that scope.
Kind'a tricky.
That would lead to something like :

function a(){
    var x = 1;
    function b(){
        alert(x);
    }
}

But that would kind of defeat the purpose.

回答8:

function a(){
   this.x = 5;
   this.obj = {..};
   var self = this;
   b(self);
}
function b(scope){
   //access x or obj....

}

回答9:

function a(){
   var x = 5;
   var obj = {..};
   var b = function()
   {
        document.println(x);
   }
   b.call();
}

回答10:

You can create your variables without the var keyword and they will be global, but no way to pass the scope that I'm aware of...

回答11:

Have you tried something like this:

function a(){
   var x = 5;
   var obj = {..};
   b(this);
}
function b(fnA){
   //access x or obj....
   fnA.obj = 6;
}

If you can stand function B as a method function A then do this:

function a(){
   var x = 5;
   var obj = {..};
   b(this);

   this.b = function (){
      // "this" keyword is still === function a
   }
}

来源：https://stackoverflow.com/questions/6348852/javascript-pass-scope-to-another-function

标签

javascript

node.js

closures

scope

serverside-javascript