JavaScript: What are .extend and .prototype used for?

by

Javascript’s inheritance is prototype based, so you extend the prototypes of objects such as Date, Math, and even your own custom ones.

Date.prototype.lol = function() {
 alert('hi');
};

( new Date ).lol() // alert message

In the snippet above, I define a method for all Date objects ( already existing ones and all new ones ).

extend is usually a high level function that copies the prototype of a new subclass that you want to extend from the base class.

So you can do something like:

extend( Fighter, Human )

And the Fighter constructor/object will inherit the prototype of Human, so if you define methods such as live and die on Human then Fighter will also inherit those.

Updated Clarification:

“high level function” meaning .extend isn’t built-in but often provided by a library such as jQuery or Prototype.

More Related Contents:

  1. Prototypical inheritance – writing up [duplicate]
  2. What are the nuances of scope prototypal / prototypical inheritance in AngularJS?
  3. Why is extending native objects a bad practice?
  4. Advantages of using prototype, vs defining methods straight in the constructor? [duplicate]
  5. Javascript object members that are prototyped as arrays become shared by all class instances
  6. Defining methods via prototype vs using this in the constructor – really a performance difference?
  7. Assigning prototype methods *inside* the constructor function – why not?
  8. JavaScript: What dangers are in extending Array.prototype?
  9. Parse JSON String into a Particular Object Prototype in JavaScript
  10. Why is mutating the [[prototype]] of an object bad for performance?
  11. JS : Convert Array of Strings to Array of Objects
  12. ES6 arrow functions not working on the prototype?
  13. Asynchronous operations in constructor
  14. Extending an Object in Javascript
  15. Javascript when to use prototypes
  16. Calling method using JavaScript prototype
  17. Create a reset of javascript Array prototype when Array.prototype has been modified?
  18. Grasping prototypical Inheritance through pseudoclassical instantiation (JavaScript)
  19. Can I construct a JavaScript object without using the new keyword?
  20. Understanding Crockford’s Object.create shim
  21. How to access object prototype in javascript?
  22. ‘this’ keyword, not clear
  23. Adding Prototype to JavaScript Object Literal
  24. Javascript: hiding prototype methods in for loop?
  25. Can you create functions with custom prototypes in JavaScript?
  26. Advantages of setting the “constructor” Property in the “prototype”
  27. What does the new keyword do under the hood?
  28. JavaScript Event prototype in IE8
  29. prototypal inheritance concept in javascript as a prototype based language
  30. ES6 – declare a prototype method on a class with an import statement

Leave a Comment