__proto__ vs prototype

• __proto__ : An internal property (getter/setter) available on every object that points to its prototype. It is deprecated in favor of Object.getPrototypeOf() / Object.setPrototypeOf() but still widely used.
• prototype : A property that exists only on constructor functions. It defines the prototype of objects created by that constructor when using new.

Code Example

function Animal() {}
Animal.prototype.sound = "grrr";

const dog = new Animal();
console.log(dog.__proto__ === Animal.prototype); // true
console.log(dog.prototype); // undefined (dog is not a constructor)