Object Comparison

A. Preface:

We usually use "==" or "===" to compare variables in JavaScript. But sometimes, the result maybe not as expected. Let's take a look:

We have class Employee:

function Employee(EmpID, Name, Birthday, Supervisor) {
    this.EmpID = EmpID;
    this.Name = Name;
    this.Birthday = Birthday;
    this.Supervisor = Supervisor;

    this.Age = function () {
        return new Date().getFullYear() - Birthday;
    }
}

 

And some instances of this class:

var Supervisor = new Employee(0, "Marry", 1979);
var Employee1 = new Employee(1, "John", 1980, Supervisor);
var Employee2 = Employee1;
var Employee3 = new Employee(1, "John", 1980, Supervisor);

 

Suppose we want to Employee1  and Employee3  are equal. We can’t use ”==” operator or ”===” operator.

alert(Employee1 == Employee2); // true. Employee1 and Employee2 are reference to ONE object in memory.
alert(Employee1 == Employee3); // false

 

B. Equal method:

So we'll define new method to compare object.

    function equals(firstObject, secondObject) {
    var property;
//Check if current object's property doesn't exist in the second one.
    for (property in firstObject) {
    if (typeof (secondObject[property]) == 'undefined'
    && typeof (firstObject[property]) != 'undefined') {
        return false;
    }
}

//Check if second object's property doesn't exist in the current one.
for (property in secondObject) {
    if (typeof (firstObject[property]) == 'undefined'
    && typeof (secondObject[property]) != 'undefined') {
        return false;
    }
}

//Compare properties value in two object
for (property in firstObject) {
    {
        switch (typeof (firstObject[property])) {
            case 'object':
            //If property is object then call method equals to compare
            if (!equals(firstObject[property], secondObject[property])) {
                return false;
            } 
            break;

            case 'function':
                //If property is function then compare content in function
                if (firstObject[property].toString() != secondObject[property].toString())
                    return false;
                break;
            default:
                //Compare value of property
                if (typeof (firstObject[property]) != typeof (secondObject[property])
                || firstObject[property] != secondObject[property])
                    return false;

        }
    }
}
return true;
}

 

C. Try it

var Supervisor = new Employee(0, "Marry", 1979);
var Employee1 = new Employee(1, "John", 1980, Supervisor);
var Employee2 = Employee1;
var Employee3 = new Employee(1, "John", 1980, Supervisor);
alert(Employee1 == Employee2); // true
alert(Employee1 == Employee3); // false
alert(equals(Employee1, Employee3)); // true

 

D. Source code

ComparingObject.js