Access inner variables from external functions in

问题:

Is it possible to access an inner variable from an external function like this example?

function a(f) {
  var c = 'test';
  f();
}

a(function() {
  alert(c);  //at this point, c should = "test"
});

回答1:

No, that won't work. What matters is where (lexically) a function is defined, not where it's invoked.

When figuring out what (if anything) "c" refers to, the language looks in the local scope, then in the next scope out based on the definition of the function. Thus if that invocation of "a" took place in another function that did have its own local "c", then that value would be what the alert showed.

function b() {
  var c = 'banana';
  a(function() {
    alert(c);  
  });
}

b(); // alert will show "banana"

回答2:

No, this is not possible. The scope you declare your anonymous function in does not have access to this c variable -- in fact, nothing but a will ever has access to c.

回答3:

No this will not work because the variable c is defined within the function and is not available outside of the function. One option though is to pass the variable c into the function provided to a

function a(f) { 
  var c = 'test'; 
  f(c); 
} 

a(function(c) { 
  alert(c);  //at this point, c should = "test" 
}); 

回答4:

As others have said, this isn't possible. You can

1. Declare the c variable outside of the scope of the function

2. Pass an argument to f:

function a(f) { var c = { name: 'test' }; f(c)  };
a(function(o) { alert(o.name) })