index.js

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

function solveRect(l,b){
    console.log("Solving for rectangle with l = " + l + " and b = " + b);

    rect(l , b , (err , rectangle) => {
        if (err){
            console.log("ERROR : " , err.message);
        }
        else{
            console.log("The area of the rectangle of dimensions l = "
                + l + " and b = " + b + " is " + rectangle.area());
            console.log("The perimeter of the rectangle of dimensions l = "
                + l + " and b = " + b + " is " + rectangle.perimeter());
        }
    });
    console.log("This statement after the call to rect()");
}

solveRect(2,4);
solveRect(3,5);
solveRect(0,5);
solveRect(-3,5);