JavaScript Engine Rules

Leadows Technologies

3 min readMar 11, 2021

1. Every object must be created from a class

2. Every object has a property __proto__

3. __proto__ of an object always refers to prototype object of the class from which the object was created

4. Every class is a function object, and hence it is created from Function class

5. As every class is a Function object, its __proto__ always refers to prototype object of Function class

6. Function class is also a Function object

7. Every class inherits Object class

8. prototype object is used for inheritance

CODE:

let assert = require("assert");// Every class has a prototype property, because every class is a function object// function object is created from the Function class
 let f1 = function () { }; 
 assert.equal(typeof f1, "function");// function object contains prototype property
 assert.notEqual(f1.prototype, undefined);// function object is created from the Function class
 assert.equal(f1.__proto__, Function.prototype);// Function class inherits Object class
 assert.equal(Function.prototype.__proto__, Object.prototype);// every function object is created from the Function class
 assert.equal(Function.__proto__, Function.prototype);// 10 is created from the Number class
 let f2 = 10;assert.equal(typeof f2, "number");// number object does not contain prototype property
 assert.equal(f2.prototype, undefined);// number object is created from the Number class
 assert.equal(f2.__proto__, Number.prototype);// Number class inherits Object class
 assert.equal(Number.prototype.__proto__, Object.prototype);// Number class/function object is created from the Function class
 assert.equal(Number.__proto__, Function.prototype);// hello is created from the String class
 let f3 = "hello"; 
 assert.equal(typeof f3, "string");// string object does not contain prototype property
 assert.equal(f3.prototype, undefined);// string object is created from the String class
 assert.equal(f3.__proto__, String.prototype);// String inherits Object class
 assert.equal(String.prototype.__proto__, Object.prototype);// String class/function object is created from the Function class
 assert.equal(String.__proto__, Function.prototype);let f4 = true; // true is created from the Boolean class
 assert.equal(typeof f4, "boolean");// boolean object does not contain prototype property
 assert.equal(f4.prototype, undefined);// boolean object is created from the Boolean class
 assert.equal(f4.__proto__, Boolean.prototype);// Boolean class inherits Object class
 assert.equal(Boolean.prototype.__proto__, Object.prototype);// Boolean class/function object is created from the Function class
 assert.equal(Boolean.__proto__, Function.prototype);let f5 = {}; // {} is created from the Object class
 assert.equal(typeof f5, "object");// { } does not have prototype property
 assert.equal(f5.prototype, undefined);// { } is created from the String class
 assert.equal(f5.__proto__, Object.prototype);// Object class/function object is created from the Function class
 assert.equal(Object.__proto__, Function.prototype);let f6 = []; // [] is created from the Array class
 assert.equal(typeof f6, "object");// [ ] does not have prototype property
 assert.equal(f6.prototype, undefined);// [ ] is created from the Array class
 assert.equal(f6.__proto__, Array.prototype);// Array inherits Object class
 assert.equal(Array.prototype.__proto__, Object.prototype);// Array class/function object is created from the Function class
 assert.equal(Array.__proto__, Function.prototype);