Question

I am writing some JavaScript profiling bits and need to be able to intercept methods inside a closure.

I managed to get this working:

var t = (function() {

  var echo = function(v) { console.log("calling echo with " + v); }; 

  return {
    intercept: function(n, f) {
      var old = eval(n);
      var newFunction = (function(that, old){
        return f(that, old);
      })(this, old);
      eval(n + " = newFunction ");
    },
    getEchoFunction: function() { return echo; }
  };  
})(); 


var c = t.getEchoFunction();

c("hello");



t.intercept("echo", function(that,old){
  return function() {
    console.log("before echo");
    old.apply(that,arguments);
    console.log("after echo");
  };
});


c = t.getEchoFunction();

c("world");

Output is:

"calling echo with hello"
"before echo"
"calling echo with world"
"after echo"

So, this “intercept” API lets me intercept and re-write function declarations hidden in a closure.

However, there is much complaining about eval in the world.

Is there any way to write the same API without needing to use eval in the intercept function?

Answer 1

No, unfortunately there is no way to access a non-global scope similar to how window[...] works.

However, depending on what you need to do using an object instead of a native scope would be a good idea.