javascript debug function using eval

Question

In C++ we can write a preprocessor macro like this:

#define DEBUG(x) cout << '>' << #x << ':' << x << endl;
int a=1;
DEBUG(a) //prints "a:1"

I tried to do a similar thing in javascript

var DEBUG= function(name){
  return function() {
      console.log(name+": ",eval(name))
  }
}
{
    let a=1;
    DEBUG('a')() //a is undefined
}

I was wondering if there was any way to "inline" functions or otherwise do some clever thing with closures which allows DEBUG to be evaluated in the calling scope. I know I could just call DEBUG('a',a) but that wouldn't be as fun ;)

All you could do is eval(debug('a')), where eval is called in the scope where the variable is available. Or you just do the same thing as in C++ and use an actual preprocessor which does macro expansion — Bergi
– Bergi, Commented Oct 12, 2017 at 2:10
@Bergi having debug return an eval string is pretty clever, I hadn't thought of that. — Akababa
– Akababa, Commented Oct 12, 2017 at 2:22

tadman · Accepted Answer · 2017-10-12 02:06:24Z

1

There's really no need for such a heavy-handed approach. You can always do this:

function debug(a) {
  console.log(a);
}

Or you can define an empty version of same with no functionality to disable it in certain run modes.

To use it is easy:

debug({ a: a, b: b });

With ES6 you can do this even more concisely:

debug({ a, b });

Couldn't be easier.

Your idea of using eval is going to fail because a is a variable that only exists inside of that specific scope due to the let declaration. That means the other function has no ability to access it.

answered Oct 12, 2017 at 2:06

tadman

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1 Comment

Akababa Over a year ago

Wow, that's pretty much exactly what I was looking for. Thanks!

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