Changing a variable out of scope?

Question

Is there a way to change a variable while out of scope? I know, in general, you cannot, but I wonder if there are any tricks or overrides. For example, is there a way to do the following work:

function blah(){ var a = 1 } a = 2; alert(blah()); 

EDIT (for clarification):

In a hypothetical scenario, the variable that is used in the setInterval function, which also goes beyond the scope and into the uneditable previous javascript file, will be changed. This is a pretty stupid scenario, but this is the one I'm going to ask about.

Answer 1

Not. No tricks or overrides. You must plan so that both places can see the variable in the same area.

The only trick I can think of regarding an area is to use the window in the browser to navigate to the global object. This can help you move on to a "hidden" variable - one that is in scope, but whose name has been overtaken by a local variable (or another variable closer to the scope chain).

Closures and classes can provide you with some other scope tricks, but none of them can completely redefine scope rules.

Answer 2

I don’t understand why you need it, if you need a variable accessible from the outside, just declare it from the outside.

Now, if you ask about it just because you are trying to find out something, it’s good for you.

 var a = 0; function blah() { a = 1; return a; } a = 2; alert(blah()); 

Answer 3

You can return a value from a function, of course:

 function blah() { var a=1; return a; } 

But I suppose that is not quite what you had in mind. Since calling a function creates a closure in local variables, it is usually not possible to change values ​​after creating a closure.

Objects are slightly different because they are reference values.

 function blah1(v) { setInterval(function() { console.log("blah1 "+v); }, 500); } function blah2(v) { setInterval(function() { console.log("blah2 "+va); }, 500); } var a = 1; var b = {a: 1}; blah1(a); blah2(b); setInterval(function() { a++; }, 2000); setInterval(function() { b.a++; }, 2000); 

If you run this in an environment with a console object, you will see that the value reported in blah2 changes after 2 seconds, but blah1 just continues to use the same value for v.

Answer 4

Functions can access variables declared outside their scope if they are declared before the function itself:

 var a = 0; function blah() { a = 1; } a = 2; alert(blah()); 

Note that using var a inside a function declared a local variable named a; here we omit the keyword, since otherwise it would hide a as announced in the outer field!

Answer 5

No, this will never work, but you can use global:

 var a; function blah(){ a = 1 } a = 2; alert(blah()); 

or use closure:

 function bleh() { var a; function blah(){ a = 1 } a = 2; alert(blah()); } 

or you can pass it with a return (which behaves differently, but this is probably what you want to do):

 function blah(a){ a = 1 return a; } a = 2; alert(blah(a));