How do you call this function in node.js ?

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Node.js

I 'm trying to figure out how to call the function square in node.js. Problem is that the square function itself expects 2 parameters , one the width and second one is another function data which is confusing to me , as i dont know how to call the a function which has another function as paramter.

square(width,function (data)
{
   console.log(data.squareVal);
});


exports.square = function(width,callback)
{
     var aa = new Object();
     callback(aa.squareVal = width * width);    
}


var s = new square(5);

console.log(s);

What I have tried:

from javascript - Node.js - use of module.exports as a constructor - Stack Overflow[^]