Having experience in Ruby, I was really happy to see closures and dynamic typing but for the life of me can’t figure out what benefits are to be had from object instances using other instances for inheritance. One of the most head-scratching elements of the languages design is its implementation of inheritance. Functions aren’t constructors, but function calls are “constructor calls” if and only if newis used.So I finally stopped dragging my feet all these years and decided to learn JavaScript “properly”. In other words, in JavaScript, it’s most appropriate to say that a “constructor” is any function called with the new keyword in front of it. The best thing to do is remind yourself, “constructor does not mean constructed by”. The words “constructor” and “prototype” only have a loose default meaning that might or might not hold true later. constructoron an object arbitrarily points, by default, at a function who, reciprocally, has a reference back to the object – a reference which it calls. Does “constructor” mean “was constructed by”? NO! constructor, and this property is a reference back to the function ( Fooin this case) that the object is associated with. The Foo.prototypeobject by default (at declaration time on line 1 of the snippet!) gets a public, non-enumerable property called. constructor = Foo // true var a = new Foo () a. If you use any other value besides a string(primitive) as the property, it will first be converted to a string. In objects, property names are **always **strings. They can also be either enumerable or not, which controls if they show up in for.inloop iterations, for instance. Properties don’t have to contain values – they can be “accessor properties” as well, with getters/setters. In addition, objects can have their mutability (and that of their properties) controlled to various levels of immutability using Object.preventExtensions(.), al(.), and eeze(.). Properties have certain characteristics that can be controlled through property descriptors, such as writableand configurable. Whenever a property is accessed, the engine actually invokes the internal default ]operation (and ]for setting values), which not only looks for the property directly on the object, but which will traverse the ]chain (see Chapter 5) if not found. The values can be accessed as properties, via. Objects are collections of key/value pairs.
#You dont know js prototypal inheritance code#
To perform operations on it, such as checking its length, accessing its individual character contents, etc, a Stringobject is required.the language automatically coerces a "string"primitive to a Stringobject when necessary, which means you almost never need to explicitly create the Object form.įunctions are callable objects which are special in that they have an optional name property and a code property (which is the body of the function that actually does stuff).Įxcluding from the self-defined object, we can always use typeof first to check out the primary types and then use instanceof to find out its object sub-types. The primitive value "I am a string"is not an object, it’s a primitive literal and immutable value. Each of these built-in functions can be used as a constructor (that is, a function call with the new operator), with the result being a newly constructed object of the sub-type. In JS, object sub-types are actually just built-in functions. Objects have sub-types, including function, and also can be behavior-specialized, like as the internal label representing the array object sub-type. Objects are one of the 6 (or 7, depending on your perspective) primitive types.
Many people mistakenly claim “everything in JavaScript is an object”, but this is incorrect. Source: You Don’t Know JS: this & Object Prototypes - Chapter 3: Objects 1.
#You dont know js prototypal inheritance how to#
What’s process of method lookup via prototype chain?
What’s the difference between _proto_ and prototype? You Don’t Know JS: this & Object Prototypes You Don't Know JS: this & Object Prototypes