Here we have a car object with a property named color , with value blue. Labels can be any string, but beware of special characters - if I wanted to include a character not valid as a variable name in the property name, I would have had to use quotes around it:.
The second which is the only one we can use for properties with invalid names , is to use square brackets:. Functions can be assigned to a function property, and in this case they are called methods.
In this example, the start property has a function assigned, and we can invoke it by using the dot syntax we used for properties, with the parentheses at the end:. In the following example, we have access to the brand and model properties values using this.
It's important to note this distinction between regular functions and arrow functions - we don't have access to this if we use an arrow function:. We can create a class named Person note the capital P , a convention when using classes , that has a name property:.
There is a special method called constructor that we can use to initialize the class properties when we create a new object instance. Now we can instantiate a new object from the class, pass in a string, and when we call hello we'll get a personalized message:.
When the object is initialized, the constructor method is called with any parameters passed. A class can extend another class, and objects initialized using that class inherit all the methods of both classes. Now if we instantiate a new object with the class Programmer , it has access to the hello method:. One of the simplest examples of how to use callbacks is with timers.
Timers are not part of JavaScript, but they are provided by the browser and Node. Let me talk about one of the timers we have: setTimeout.
The setTimeout function accepts 2 arguments: a function, and a number. The number is the milliseconds that must pass before the function is ran.
The function containing the console. If you add a console. This is a very common pattern when working with the file system, the network, events, or the DOM in the browser.
As we saw in the previous chapter, with callbacks we'd be passing a function to another function call that would be called when the function has finished processing. The main problem with this approach is that if we need to use the result of this function in the rest of our code, all our code must be nested inside the callback, and if we have to do callbacks we enter in what is usually defined "callback hell" with many levels of functions indented into other functions:.
We first call the function, then we have a then method that is called when the function ends. Now, to be able to use this syntax, the doSomething function implementation must be a little bit special.
It must use the Promises API. This function receives 2 parameters. The first is a function we call to resolve the promise, the second a function we call to reject the promise. Resolving a promise means to complete it successfully which results in calling the then method in whatever uses it.
Rejecting a promise means ending it with an error which results in calling the catch method in whatever uses it. Any code that wants to use this function will use the await keyword right before the function:. With one particular caveat: whenever we use the await keyword, we must do so inside a function defined as async.
As you can see in the example above, our code looks very simple. Compare it to code using promises, or callback functions. And this is a very simple example, the major benefits will arise when the code is much more complex. When I introduced variables, I talked about using const , let , and var. If a variable is defined outside of a function or block, it's attached to the global object and it has a global scope, which mean it's available in every part of a program. There is a very important difference between var , let and const declarations.
A variable defined as var inside a function is only visible inside that function, similar to a function's arguments. A variable defined as const or let on the other hand is only visible inside the block where it is defined. A block is a set of instructions grouped into a pair of curly braces, like the ones we can find inside an if statement, a for loop, or a function.
It's important to understand that a block does not define a new scope for var , but it does for let and const. Suppose you define a var variable inside an if conditional in a function. This is because var is function scoped, and there's a special thing happening here called hoisting. In short, the var declaration is moved to the top of the closest function by JavaScript before it runs the code.
This is what the function looks like to JS internally, more or less:. This is why you can also console. It can be tricky at first, but once you realize this difference, then you'll see why var is considered a bad practice nowadays compared to let - they have less moving parts, and their scope is limited to the block, which also makes them very good as loop variables because they cease to exist after a loop has ended:.
If you switch to let , when you try to console. If this article was helpful, tweet it. Learn to code for free. Get started. Forum Donate. Flavio Copes. JavaScript is one of the most popular programming languages in the world. I believe it's a great choice for your first programming language ever.
We mainly use JavaScript to create websites web applications server-side applications using Node. JavaScript is a programming language that is: high level : it provides abstractions that allow you to ignore the details of the machine where it's running on.
It manages memory automatically with a garbage collector, so you can focus on the code instead of managing memory like other languages like C would need, and provides many constructs which allow you to deal with highly powerful variables and objects. This has pros and cons, and it gives us powerful features like dynamic typing, late binding, reflection, functional programming, object runtime alteration, closures and much more.
Don't worry if those things are unknown to you - you'll know all of them by the end of the course. You can reassign any type to a variable, for example, assigning an integer to a variable that holds a string. In practice, browsers do compile JavaScript before executing it, for performance reasons, but this is transparent to you - there is no additional step involved.
You can write JavaScript using an object-oriented paradigm, using prototypes and the new as of ES6 classes syntax. You can write JavaScript in a functional programming style, with its first-class functions, or even in an imperative style C-like. A little bit of history Created in , JavaScript has gone a very long way since its humble beginnings.
Just JavaScript Sometimes it's hard to separate JavaScript from the features of the environment it is used in. In this book I talk about JavaScript, the language. This book does not try to cover everything under the sun related to JavaScript. It focuses on the core of the language, trying to simplify the more complex topics. The author hopes the contents of this book will help you achieve what you want: learn the basics of JavaScript.
The React Beginner's Handbook. This book does not try to cover everything under the sun related to React. To describe the way the JavaScript language should work so that the various pieces of software that claimed to support JavaScript were actually talking aboutthesamelanguage.
Download free JavaScript eBooks in pdf format or read books online. Feel free to comment, ask questions if you have any doubt. Pages Home core java spring online courses thread java 8 coding sql books oop interview certification free resources best. The internet is full of good things, and one of them is free eBooks and PDF. Programmers can almost run anything by these free books. Earlier I have shared some of the free JavaScript tutorials , and in this article, I am going to share 5 good books to learn JavaScript, which are open to read online or allow you to download PDF for offline reading.
JavaScript is probably another language I recommend someone who knows Java, Why?
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