JavaScript pass scope to another function
what about using bind
function funcA(param) {
var bscoped = funcB.bind(this);
bscoped(param1,param2...)
}
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.
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()
}
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 ofa
.function a() { var x = 5, obj = {}; function b(){ // access x or obj... } b(); } a();
If you don't want
b
inside ofa
, 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 accessa
'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 ofa
, but this way they are only accessible if explicitly given out from withina
.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();