Callback example

app.js

var rect = require('./module');

function solveRect(l,b) {
    console.log("Solving for rectangle with l = " + l + " and b = " + b);
    rect(l,b, function(err,rectangle) {
        if (err) {
	        console.log(err);
    	}
    	else {
    	    console.log("The area of a rectangle of dimensions length = " + l + " and breadth = " + b + " is " + rectangle.area());
            console.log("The perimeter of a rectangle of dimensions length = " + l + " and breadth = " + b + " is " + rectangle.perimeter());
    	}
    });
};

solveRect(-3,5);

module.js

module.exports = function(x,y,callback) {
  try {
      if (x < 0 || y < 0) {
          throw new Error("Rectangle dimensions should be > 0: l = " + x + ", and b = " + y);
      }
      else
          callback(null, {
              perimeter: function () {
                  return (2*(x+y));
              },
                  area:function () {
                  return (x*y);
              }
          });
  }
  catch (error) {
      callback(error,null);
  }
}