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I've been doing JavaScript for quite a while now and I come from a. NET and Java background. And what's always amazing to me is when I have object-oriented developers who do really good. NET and Java code, move over to JavaScript, and lose all that object-oriented knowledge and start writing very procedural JavaScript code. And in this course, I'm going to try and undo some of that and show you how to properly implement good, solid, object-oriented development styles into JavaScript.

We'll take a look at objects in JavaScript and why they're different. And then we'll move into the full Gang of Four design patterns and we'll look at what those look like in the JavaScript ecosystem. We'll look at creational design patterns and structural, and then, even behavioral, just so that you can get a good solid understanding of how to adapt your JavaScript code to be much more object-oriented.

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We can call myRevealingModule. Advantages of Revealing Module pattern over Module Pattern:. But with ES6, JavaScript has native modules. ES6 modules are stored in files. There can only be one module per file. Everything inside a module is private by default. Functions, variables, and classes are exposed using the export keyword. The code inside a module always runs in strict mode. There are two ways to export a function and variable declaration:.

Similar to exporting a module, there are two ways to import a module by using the import keyword. If you want to avoid naming collisions, you can change the name of export both during export as well as import. A Singleton is an object which can only be instantiated only once. If an instance exists, it simply returns a reference to that object.

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Any repeated calls to the constructor would always fetch the same object. JavaScript has always had singletons built-in to the language.

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Because each object in JavaScript occupies a unique memory location and when we call the user object, we are essentially returning reference to this object. If we try to copy the user variable into another variable and modify that variable. We would see both of objects are modified because objects in JavaScript are passed by reference not by value.

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  5. So there is only a single object in the memory. Singleton pattern can be implemented using the constructor function. When this constructor function is called, it checks if the instance object exists or not.

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    And if the object exists, it just returns that object. Singletons can also be implemented using the module pattern. In the above code, we are creating a new instance by calling the singleton. Factory Pattern is a pattern that uses factory methods to create objects without specifying the exact class or constructor function from which the object will be created.

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    Top 10 JavaScript Patterns Every Developer Likes

    The factory pattern is used to create objects without exposing the instantiation logic. This pattern can be used when we need to generate a different object depending upon a specific condition. Here I have created a Car and a Truck class with some default values which is used to create new car and truck objects.

    And I have defined a VehicleFactory class to create and return a new object based on vehicleType property received in the options object. Since callbacks are just functions, they are supported by all the environments that run JavaScript, from our browsers to servers that run Node. Simple, but yet powerful, this pattern is fundamental in asynchrony.

    However, it also has its drawbacks. When projects start to grow and we need to start doing more complex code, it becomes harder to implement generic solutions on our programs, making them harder to read and maintain. This is usually known as "Callback Hell".

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    However, the worst that we can have with callbacks is the inversion of control. If this happens, we are giving control of the program flow sequence to other parties, making it difficult or even impossible!

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    Promises are harder to master, but address the inversion of control issue. They are a little slower than callbacks, but in return we get a lot of trustability. Promises are a trustable mechanism that also help expressing async code in a more sequential way. They can have, at most, one resolution value, meaning that a Promise always needs to be resolved or rejected. This is how they solve the inversion of control.

    Not by removing callbacks, but by creating a mechanism on the wrapper that handles this issue. Promises provide more functionality, like, for example, the Promise. With this kind of operations we can start multiple async requests and proceed only when all of them are resolved or when the first finishes. Also, we can chain multiple Promises on our code without forcing a new level of indentation after each one, using.

    Modular Javascript #3 - Revealing Module Pattern Javascript Tutorial

    This improves the readability of the code, and the maintainability of the program as well, but not everything is perfect. Since this feature is at framework level, there are multiple implementations that can vary on behavior, plus the overhead cost of time and memory. Generators were introduced on ECMAScript and are functions in which we can use and control the iterator, meaning that functions can be paused and resumed at any time. This is a powerful tool for when we want to get each value only when we need, instead of getting all of them at once. We can see in this example that for each next we receive an object with the value and a flag indicating if the generator functions ended.

    But generators can be used to control async flows in conjugations with other libraries as well, like in co or redux-saga , of which I will talk more about further ahead.