key is the property name, as a string, that we’re applying the decorator to. Functions can be used to somewhat simulate classes, but in general JavaScript is a class-less language. In order to compare them, I’ll create the same object definition (TodoModel) as a class, and then as a factory function. Functions and methods both are functions in JavaScript. And when it comes to inheritance, objects inherit from objects, not classes from classes as in the "class"-ical languages. Keep in mind that returning object literals using the concise body syntax params => {object:literal} will not work as expected. No - it’s simply another way of structuring and organizing your code. It is JavaScript after all. So what’s functional programming then? That’s because JavaScript doesn’t have a concept of methods. TodoModel as a Class Discover Functional JavaScript was named one of the best new Functional Programming books by BookAuthority!. A class constructor creates an instance of the class. Sometimes people will refer to them as reference types, classes, data types, or simply constructors. JavaScript Constructor Functions and Classes. If you remember the javascript prototype chaining we were doing a few years ago which mocked the class behavior, the class syntax was a natural next evolution in syntax. A constructor in JavaScript is just a plain old function that returns an object. ; Mostly, the second approach is preferred, so that every “thing” resides in its own module. As a downside, you have the overhead of writing and using classes as well as maybe some issues with the this keyword in some cases. Today, most languages support both procedural and functional programming (Scala, C# 2.5 +, Java 8 and Php 5.3+ for example) but JavaScript takes the best of both worlds. Procedural programming typically involves your code executing at the top of your script and going in order, statement by statement, to the bottom. 1. Everything is an object. var func = => {foo: 1}; // Calling func() returns undefined! What we do inside of the decorator function depends on the purpose of our decorator. The private variables, and functions are defined with the keyword "var". JS decorator functions are passed three arguments: target is the class that our object is an instance of. Classes Are Functions. Classes are declared with the class keyword. // Initializing a function with a function expression const x = function() {} It's important to note that there are no classes in JavaScript. a module user.js exports only class User. Modules that contain a library, pack of functions, like say.js above. Even though javascript is a 'functional' language, I would bet that most javascript developers write OO code. These are typically arrow functions but can also be created with the regular function keyword. A method is just a function which is a property of an object. var func = => {foo: function {}}; // SyntaxError: function statement requires a name. descriptor is that property’s descriptor object. ECMAScript 2015 (aka ES6) comes with the class syntax, so now we have two competing patterns for creating objects. Constructor Functions. Constructor functions are the equivalent of classes in many programming languages. This is because the code inside braces ({}) is parsed as a sequence of statements (i.e. In practice, there are mainly two kinds of modules. We will use function expression syntax to initialize a function and class expression syntax to initialize a class. A class in JavaScript is created with the special word: function, using this syntax: className = function() { // code of the className class } A class can contain public and private variables (called also properties) and functions (also called methods). 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