Saturday, April 16, 2011

Lazy Logging on Javascript (2)

A few weeks ago, I wrote about how to do lazy logging in Javascript by passing functions to the logging functions. These functions would actually do the CPU intensive evaluation (if needed) and return something that would subsequently be printed on the screen. The key thing to notice is that the item(s) to be printed would be computed ONLY if they were actually going to be printed (using the current logging level and the 1st parameter to the logging function).

I noticed that a lot of code had started looking quite ugly.
log_it("DEBUG", function() {
  return [ some_var1.toString(), some_var2.toString() ];

Note: Any expensive computation that should be performed MUST go inside the toString() method of some_var1 and some_var2.

I have instead decided to solve it by making a function do what the caller was earlier doing:
// toString() Promise
function tsp() {
  var args = arguments;
  return {
    toString: function() {
      return {
        return v.toString();
      }).join(' ');

As a result of this modification, all code that does logging now looks like this:
log_it("DEBUG", tsp(some_var1, some_var2));

The reason why this works is because log_it() is going to call toString() (if required) on each of its arguments before printing them.

Much neater eh?