Javascript - Object Equality

About

For a comparison between object, both == and === object equality operator will simply check whether the references match, not anything about the underlying values.

valueOf is called if one side of the equality comparison is not an object.

Example

Object

function Employee(name) {
    this.name = name;
    this.dept = 'general';
    this.valueOf = function(){
        return this.name;
    };
}
let employee1 = new Employee('nico');
let employee2 = new Employee('nico');
  • Test
console.log("The variable employee1 has the type "+(typeof employee1 ));
console.log("The variable employee1 has the valueOf "+employee1.valueOf());
console.log("They are not equal "+(employee1 == employee2));
console.log("But their value is "+(employee1.valueOf() == employee2.valueOf()));

Array

var a = [1,2,3];  
var b = [1,2,3]; 
console.log("The array a has the type "+(typeof a));
console.log("The array a in a string format is "+a.toString()+ "( valueOf() )" );
  • The string representation of an array is element1, …, elementn
var c = "1,2,3"; 
console.log("The variable c has the type "+(typeof c));
  • Equality
console.log("\nEquality");
console.log( a == c ); // true - same value as string
console.log( b == c ); // true - same value as string
console.log( a == b ); // false (not the same reference)

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