• When you want to implement inheritance, you attach properties and methods to the prototype

  • Every JS function has a prototype property

    • The prototype property is empty by default

    • The prototype property is not enumerable

  • Every JS object has a prototype attribute

    • Points to the object's parent

    • Set automatically when the object is created

  • All JS objects inherit the following properties and methods from Object.prototype:

    • constructor

    • hasOwnProperty()

    • isPrototypeOf()

    • propertyIsEnumerable()

    • toLocaleString()

    • toString()

    • valueOf()


  • Functions used for initializing new objects

  • Called using the new keyword

  • All objects inherit a constructor property that points to the constructor of the object

  • If an object is created with an object literal, it inherits from Object.prototype; if an object is created from a constructor, it inherits from the constructor


  • Every object's prototype is either null or references another object

  • The prototype property is internal and hidden, though there's a few ways to access it

    • You can use myObject.__proto__

      • This is a historical getter/setter

      • Has been replaced with Object.getPrototypeOf and Object.setPrototypeOf

  • Prototypes are only used for reading

    • All write/delete operations operate directly on the object

    • Accessor functions are an exception, since calling a setter is technically writing

  • The this keyword is not affected by prototypes

  • Currently, the recommended way of setting the prototype of an object is Object.create

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