Object comparison in Javascript

compare.js

// Based on: http://stackoverflow.com/questions/14368596/how-can-i-check-that-two-objects-have-the-same-set-of-property-names
Object.prototype.isIdenticalTo = function(targetObject) {

    // check that targetObject is an object
    // if no argument is passed and it's not an object
    // throw an error
    
    if (!targetObject || typeof(targetObject) !== "object") {
        throw new Error("Argument of type Object must be passed")
    }

    let objKeys         = Object.keys(this).sort()
    let targetKeys      = Object.keys(targetObject).sort()

    return JSON.stringify(objKeys) === JSON.stringify(targetKeys)
}

let obj     = {name: "karim benz", club: "Real Madrid CF"}
let obj2    = { club: "Real Madrid CF", name: "karim benz"}

console.log(obj.isIdenticalTo(obj2)) // Should return true

obj2['shirtNo'] = 9

console.log(obj.isIdenticalTo(obj2)) // Should return false
console.log(obj.isIdenticalTo())     // Should return an error