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javascriptprototype

Why __proto__ is the same

Why different objects have the same proto with the same assigned properties?

For example:

let a1 = {name: 'firstName'};
let a2 = {name: 'middleName'};
let a3 = Object.assign({}, {name: 'lastName'});

a1.__proto__ === a2.__proto__  // true
a1.__proto__ === a3.__proto__  // true

But if I use constructor function:

let SomeFunc = function(){}
let b1 = new SomeFunc();
b1.__proto__ === a1.__proto__ // false
The __proto__ is different

It looks that all projects created with direct project syntax have the same proto.

Solution

  • Because all the three objects inherit from the same prototype object, Object.prototype. That's the default for objects created from object literals.

    In your second example, b1 does inherit from SomeFunc.prototype, because it was created with the new operator. It would be the same as that of const b2 = new SomeFunct: Object.getPrototypeOf(b2) === Object.getPrototypeOf(b1).